diff --git a/Android.bp b/Android.bp
new file mode 100644
index 0000000..e91fcf1
--- /dev/null
+++ b/Android.bp
@@ -0,0 +1,29 @@
+//
+// Copyright (C) 2022 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package {
+    default_applicable_licenses: ["external_python_typing_license"],
+}
+
+license {
+    name: "external_python_typing_license",
+    visibility: [":__subpackages__"],
+    license_kinds: [
+        "SPDX-license-identifier-MIT",
+    ],
+    license_text: [
+        "LICENSE",
+    ],
+}
diff --git a/typing_extensions/Android.bp b/typing_extensions/Android.bp
new file mode 100644
index 0000000..33b5f83
--- /dev/null
+++ b/typing_extensions/Android.bp
@@ -0,0 +1,34 @@
+// Copyright 2022 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package {
+    default_applicable_licenses: ["external_python_typing_license"],
+}
+
+python_library {
+    name: "typing_extensions",
+    host_supported: true,
+    srcs: [
+       "__init__.py",
+        "src/typing_extensions.py",
+    ],
+    version: {
+        py2: {
+            enabled: false,
+        },
+        py3: {
+            enabled: true,
+        },
+    },
+    pkg_path: "typing_extensions",
+}
diff --git a/typing_extensions/__init__.py b/typing_extensions/__init__.py
new file mode 100644
index 0000000..036ff06
--- /dev/null
+++ b/typing_extensions/__init__.py
@@ -0,0 +1,2907 @@
+import abc
+import collections
+import collections.abc
+import operator
+import sys
+import types as _types
+import typing
+
+# After PEP 560, internal typing API was substantially reworked.
+# This is especially important for Protocol class which uses internal APIs
+# quite extensively.
+PEP_560 = sys.version_info[:3] >= (3, 7, 0)
+
+if PEP_560:
+    GenericMeta = type
+else:
+    # 3.6
+    from typing import GenericMeta, _type_vars  # noqa
+
+
+# Please keep __all__ alphabetized within each category.
+__all__ = [
+    # Super-special typing primitives.
+    'ClassVar',
+    'Concatenate',
+    'Final',
+    'LiteralString',
+    'ParamSpec',
+    'Self',
+    'Type',
+    'TypeVarTuple',
+    'Unpack',
+
+    # ABCs (from collections.abc).
+    'Awaitable',
+    'AsyncIterator',
+    'AsyncIterable',
+    'Coroutine',
+    'AsyncGenerator',
+    'AsyncContextManager',
+    'ChainMap',
+
+    # Concrete collection types.
+    'ContextManager',
+    'Counter',
+    'Deque',
+    'DefaultDict',
+    'OrderedDict',
+    'TypedDict',
+
+    # Structural checks, a.k.a. protocols.
+    'SupportsIndex',
+
+    # One-off things.
+    'Annotated',
+    'assert_never',
+    'dataclass_transform',
+    'final',
+    'IntVar',
+    'is_typeddict',
+    'Literal',
+    'NewType',
+    'overload',
+    'Protocol',
+    'reveal_type',
+    'runtime',
+    'runtime_checkable',
+    'Text',
+    'TypeAlias',
+    'TypeGuard',
+    'TYPE_CHECKING',
+    'Never',
+    'NoReturn',
+    'Required',
+    'NotRequired',
+]
+
+if PEP_560:
+    __all__.extend(["get_args", "get_origin", "get_type_hints"])
+
+# The functions below are modified copies of typing internal helpers.
+# They are needed by _ProtocolMeta and they provide support for PEP 646.
+
+
+def _no_slots_copy(dct):
+    dict_copy = dict(dct)
+    if '__slots__' in dict_copy:
+        for slot in dict_copy['__slots__']:
+            dict_copy.pop(slot, None)
+    return dict_copy
+
+
+_marker = object()
+
+
+def _check_generic(cls, parameters, elen=_marker):
+    """Check correct count for parameters of a generic cls (internal helper).
+    This gives a nice error message in case of count mismatch.
+    """
+    if not elen:
+        raise TypeError(f"{cls} is not a generic class")
+    if elen is _marker:
+        if not hasattr(cls, "__parameters__") or not cls.__parameters__:
+            raise TypeError(f"{cls} is not a generic class")
+        elen = len(cls.__parameters__)
+    alen = len(parameters)
+    if alen != elen:
+        if hasattr(cls, "__parameters__"):
+            parameters = [p for p in cls.__parameters__ if not _is_unpack(p)]
+            num_tv_tuples = sum(isinstance(p, TypeVarTuple) for p in parameters)
+            if (num_tv_tuples > 0) and (alen >= elen - num_tv_tuples):
+                return
+        raise TypeError(f"Too {'many' if alen > elen else 'few'} parameters for {cls};"
+                        f" actual {alen}, expected {elen}")
+
+
+if sys.version_info >= (3, 10):
+    def _should_collect_from_parameters(t):
+        return isinstance(
+            t, (typing._GenericAlias, _types.GenericAlias, _types.UnionType)
+        )
+elif sys.version_info >= (3, 9):
+    def _should_collect_from_parameters(t):
+        return isinstance(t, (typing._GenericAlias, _types.GenericAlias))
+else:
+    def _should_collect_from_parameters(t):
+        return isinstance(t, typing._GenericAlias) and not t._special
+
+
+def _collect_type_vars(types, typevar_types=None):
+    """Collect all type variable contained in types in order of
+    first appearance (lexicographic order). For example::
+
+        _collect_type_vars((T, List[S, T])) == (T, S)
+    """
+    if typevar_types is None:
+        typevar_types = typing.TypeVar
+    tvars = []
+    for t in types:
+        if (
+            isinstance(t, typevar_types) and
+            t not in tvars and
+            not _is_unpack(t)
+        ):
+            tvars.append(t)
+        if _should_collect_from_parameters(t):
+            tvars.extend([t for t in t.__parameters__ if t not in tvars])
+    return tuple(tvars)
+
+
+# 3.6.2+
+if hasattr(typing, 'NoReturn'):
+    NoReturn = typing.NoReturn
+# 3.6.0-3.6.1
+else:
+    class _NoReturn(typing._FinalTypingBase, _root=True):
+        """Special type indicating functions that never return.
+        Example::
+
+          from typing import NoReturn
+
+          def stop() -> NoReturn:
+              raise Exception('no way')
+
+        This type is invalid in other positions, e.g., ``List[NoReturn]``
+        will fail in static type checkers.
+        """
+        __slots__ = ()
+
+        def __instancecheck__(self, obj):
+            raise TypeError("NoReturn cannot be used with isinstance().")
+
+        def __subclasscheck__(self, cls):
+            raise TypeError("NoReturn cannot be used with issubclass().")
+
+    NoReturn = _NoReturn(_root=True)
+
+# Some unconstrained type variables.  These are used by the container types.
+# (These are not for export.)
+T = typing.TypeVar('T')  # Any type.
+KT = typing.TypeVar('KT')  # Key type.
+VT = typing.TypeVar('VT')  # Value type.
+T_co = typing.TypeVar('T_co', covariant=True)  # Any type covariant containers.
+T_contra = typing.TypeVar('T_contra', contravariant=True)  # Ditto contravariant.
+
+ClassVar = typing.ClassVar
+
+# On older versions of typing there is an internal class named "Final".
+# 3.8+
+if hasattr(typing, 'Final') and sys.version_info[:2] >= (3, 7):
+    Final = typing.Final
+# 3.7
+elif sys.version_info[:2] >= (3, 7):
+    class _FinalForm(typing._SpecialForm, _root=True):
+
+        def __repr__(self):
+            return 'typing_extensions.' + self._name
+
+        def __getitem__(self, parameters):
+            item = typing._type_check(parameters,
+                                      f'{self._name} accepts only single type')
+            return typing._GenericAlias(self, (item,))
+
+    Final = _FinalForm('Final',
+                       doc="""A special typing construct to indicate that a name
+                       cannot be re-assigned or overridden in a subclass.
+                       For example:
+
+                           MAX_SIZE: Final = 9000
+                           MAX_SIZE += 1  # Error reported by type checker
+
+                           class Connection:
+                               TIMEOUT: Final[int] = 10
+                           class FastConnector(Connection):
+                               TIMEOUT = 1  # Error reported by type checker
+
+                       There is no runtime checking of these properties.""")
+# 3.6
+else:
+    class _Final(typing._FinalTypingBase, _root=True):
+        """A special typing construct to indicate that a name
+        cannot be re-assigned or overridden in a subclass.
+        For example:
+
+            MAX_SIZE: Final = 9000
+            MAX_SIZE += 1  # Error reported by type checker
+
+            class Connection:
+                TIMEOUT: Final[int] = 10
+            class FastConnector(Connection):
+                TIMEOUT = 1  # Error reported by type checker
+
+        There is no runtime checking of these properties.
+        """
+
+        __slots__ = ('__type__',)
+
+        def __init__(self, tp=None, **kwds):
+            self.__type__ = tp
+
+        def __getitem__(self, item):
+            cls = type(self)
+            if self.__type__ is None:
+                return cls(typing._type_check(item,
+                           f'{cls.__name__[1:]} accepts only single type.'),
+                           _root=True)
+            raise TypeError(f'{cls.__name__[1:]} cannot be further subscripted')
+
+        def _eval_type(self, globalns, localns):
+            new_tp = typing._eval_type(self.__type__, globalns, localns)
+            if new_tp == self.__type__:
+                return self
+            return type(self)(new_tp, _root=True)
+
+        def __repr__(self):
+            r = super().__repr__()
+            if self.__type__ is not None:
+                r += f'[{typing._type_repr(self.__type__)}]'
+            return r
+
+        def __hash__(self):
+            return hash((type(self).__name__, self.__type__))
+
+        def __eq__(self, other):
+            if not isinstance(other, _Final):
+                return NotImplemented
+            if self.__type__ is not None:
+                return self.__type__ == other.__type__
+            return self is other
+
+    Final = _Final(_root=True)
+
+
+if sys.version_info >= (3, 11):
+    final = typing.final
+else:
+    # @final exists in 3.8+, but we backport it for all versions
+    # before 3.11 to keep support for the __final__ attribute.
+    # See https://bugs.python.org/issue46342
+    def final(f):
+        """This decorator can be used to indicate to type checkers that
+        the decorated method cannot be overridden, and decorated class
+        cannot be subclassed. For example:
+
+            class Base:
+                @final
+                def done(self) -> None:
+                    ...
+            class Sub(Base):
+                def done(self) -> None:  # Error reported by type checker
+                    ...
+            @final
+            class Leaf:
+                ...
+            class Other(Leaf):  # Error reported by type checker
+                ...
+
+        There is no runtime checking of these properties. The decorator
+        sets the ``__final__`` attribute to ``True`` on the decorated object
+        to allow runtime introspection.
+        """
+        try:
+            f.__final__ = True
+        except (AttributeError, TypeError):
+            # Skip the attribute silently if it is not writable.
+            # AttributeError happens if the object has __slots__ or a
+            # read-only property, TypeError if it's a builtin class.
+            pass
+        return f
+
+
+def IntVar(name):
+    return typing.TypeVar(name)
+
+
+# 3.8+:
+if hasattr(typing, 'Literal'):
+    Literal = typing.Literal
+# 3.7:
+elif sys.version_info[:2] >= (3, 7):
+    class _LiteralForm(typing._SpecialForm, _root=True):
+
+        def __repr__(self):
+            return 'typing_extensions.' + self._name
+
+        def __getitem__(self, parameters):
+            return typing._GenericAlias(self, parameters)
+
+    Literal = _LiteralForm('Literal',
+                           doc="""A type that can be used to indicate to type checkers
+                           that the corresponding value has a value literally equivalent
+                           to the provided parameter. For example:
+
+                               var: Literal[4] = 4
+
+                           The type checker understands that 'var' is literally equal to
+                           the value 4 and no other value.
+
+                           Literal[...] cannot be subclassed. There is no runtime
+                           checking verifying that the parameter is actually a value
+                           instead of a type.""")
+# 3.6:
+else:
+    class _Literal(typing._FinalTypingBase, _root=True):
+        """A type that can be used to indicate to type checkers that the
+        corresponding value has a value literally equivalent to the
+        provided parameter. For example:
+
+            var: Literal[4] = 4
+
+        The type checker understands that 'var' is literally equal to the
+        value 4 and no other value.
+
+        Literal[...] cannot be subclassed. There is no runtime checking
+        verifying that the parameter is actually a value instead of a type.
+        """
+
+        __slots__ = ('__values__',)
+
+        def __init__(self, values=None, **kwds):
+            self.__values__ = values
+
+        def __getitem__(self, values):
+            cls = type(self)
+            if self.__values__ is None:
+                if not isinstance(values, tuple):
+                    values = (values,)
+                return cls(values, _root=True)
+            raise TypeError(f'{cls.__name__[1:]} cannot be further subscripted')
+
+        def _eval_type(self, globalns, localns):
+            return self
+
+        def __repr__(self):
+            r = super().__repr__()
+            if self.__values__ is not None:
+                r += f'[{", ".join(map(typing._type_repr, self.__values__))}]'
+            return r
+
+        def __hash__(self):
+            return hash((type(self).__name__, self.__values__))
+
+        def __eq__(self, other):
+            if not isinstance(other, _Literal):
+                return NotImplemented
+            if self.__values__ is not None:
+                return self.__values__ == other.__values__
+            return self is other
+
+    Literal = _Literal(_root=True)
+
+
+_overload_dummy = typing._overload_dummy  # noqa
+overload = typing.overload
+
+
+# This is not a real generic class.  Don't use outside annotations.
+Type = typing.Type
+
+# Various ABCs mimicking those in collections.abc.
+# A few are simply re-exported for completeness.
+
+
+class _ExtensionsGenericMeta(GenericMeta):
+    def __subclasscheck__(self, subclass):
+        """This mimics a more modern GenericMeta.__subclasscheck__() logic
+        (that does not have problems with recursion) to work around interactions
+        between collections, typing, and typing_extensions on older
+        versions of Python, see https://github.com/python/typing/issues/501.
+        """
+        if self.__origin__ is not None:
+            if sys._getframe(1).f_globals['__name__'] not in ['abc', 'functools']:
+                raise TypeError("Parameterized generics cannot be used with class "
+                                "or instance checks")
+            return False
+        if not self.__extra__:
+            return super().__subclasscheck__(subclass)
+        res = self.__extra__.__subclasshook__(subclass)
+        if res is not NotImplemented:
+            return res
+        if self.__extra__ in subclass.__mro__:
+            return True
+        for scls in self.__extra__.__subclasses__():
+            if isinstance(scls, GenericMeta):
+                continue
+            if issubclass(subclass, scls):
+                return True
+        return False
+
+
+Awaitable = typing.Awaitable
+Coroutine = typing.Coroutine
+AsyncIterable = typing.AsyncIterable
+AsyncIterator = typing.AsyncIterator
+
+# 3.6.1+
+if hasattr(typing, 'Deque'):
+    Deque = typing.Deque
+# 3.6.0
+else:
+    class Deque(collections.deque, typing.MutableSequence[T],
+                metaclass=_ExtensionsGenericMeta,
+                extra=collections.deque):
+        __slots__ = ()
+
+        def __new__(cls, *args, **kwds):
+            if cls._gorg is Deque:
+                return collections.deque(*args, **kwds)
+            return typing._generic_new(collections.deque, cls, *args, **kwds)
+
+ContextManager = typing.ContextManager
+# 3.6.2+
+if hasattr(typing, 'AsyncContextManager'):
+    AsyncContextManager = typing.AsyncContextManager
+# 3.6.0-3.6.1
+else:
+    from _collections_abc import _check_methods as _check_methods_in_mro  # noqa
+
+    class AsyncContextManager(typing.Generic[T_co]):
+        __slots__ = ()
+
+        async def __aenter__(self):
+            return self
+
+        @abc.abstractmethod
+        async def __aexit__(self, exc_type, exc_value, traceback):
+            return None
+
+        @classmethod
+        def __subclasshook__(cls, C):
+            if cls is AsyncContextManager:
+                return _check_methods_in_mro(C, "__aenter__", "__aexit__")
+            return NotImplemented
+
+DefaultDict = typing.DefaultDict
+
+# 3.7.2+
+if hasattr(typing, 'OrderedDict'):
+    OrderedDict = typing.OrderedDict
+# 3.7.0-3.7.2
+elif (3, 7, 0) <= sys.version_info[:3] < (3, 7, 2):
+    OrderedDict = typing._alias(collections.OrderedDict, (KT, VT))
+# 3.6
+else:
+    class OrderedDict(collections.OrderedDict, typing.MutableMapping[KT, VT],
+                      metaclass=_ExtensionsGenericMeta,
+                      extra=collections.OrderedDict):
+
+        __slots__ = ()
+
+        def __new__(cls, *args, **kwds):
+            if cls._gorg is OrderedDict:
+                return collections.OrderedDict(*args, **kwds)
+            return typing._generic_new(collections.OrderedDict, cls, *args, **kwds)
+
+# 3.6.2+
+if hasattr(typing, 'Counter'):
+    Counter = typing.Counter
+# 3.6.0-3.6.1
+else:
+    class Counter(collections.Counter,
+                  typing.Dict[T, int],
+                  metaclass=_ExtensionsGenericMeta, extra=collections.Counter):
+
+        __slots__ = ()
+
+        def __new__(cls, *args, **kwds):
+            if cls._gorg is Counter:
+                return collections.Counter(*args, **kwds)
+            return typing._generic_new(collections.Counter, cls, *args, **kwds)
+
+# 3.6.1+
+if hasattr(typing, 'ChainMap'):
+    ChainMap = typing.ChainMap
+elif hasattr(collections, 'ChainMap'):
+    class ChainMap(collections.ChainMap, typing.MutableMapping[KT, VT],
+                   metaclass=_ExtensionsGenericMeta,
+                   extra=collections.ChainMap):
+
+        __slots__ = ()
+
+        def __new__(cls, *args, **kwds):
+            if cls._gorg is ChainMap:
+                return collections.ChainMap(*args, **kwds)
+            return typing._generic_new(collections.ChainMap, cls, *args, **kwds)
+
+# 3.6.1+
+if hasattr(typing, 'AsyncGenerator'):
+    AsyncGenerator = typing.AsyncGenerator
+# 3.6.0
+else:
+    class AsyncGenerator(AsyncIterator[T_co], typing.Generic[T_co, T_contra],
+                         metaclass=_ExtensionsGenericMeta,
+                         extra=collections.abc.AsyncGenerator):
+        __slots__ = ()
+
+NewType = typing.NewType
+Text = typing.Text
+TYPE_CHECKING = typing.TYPE_CHECKING
+
+
+def _gorg(cls):
+    """This function exists for compatibility with old typing versions."""
+    assert isinstance(cls, GenericMeta)
+    if hasattr(cls, '_gorg'):
+        return cls._gorg
+    while cls.__origin__ is not None:
+        cls = cls.__origin__
+    return cls
+
+
+_PROTO_WHITELIST = ['Callable', 'Awaitable',
+                    'Iterable', 'Iterator', 'AsyncIterable', 'AsyncIterator',
+                    'Hashable', 'Sized', 'Container', 'Collection', 'Reversible',
+                    'ContextManager', 'AsyncContextManager']
+
+
+def _get_protocol_attrs(cls):
+    attrs = set()
+    for base in cls.__mro__[:-1]:  # without object
+        if base.__name__ in ('Protocol', 'Generic'):
+            continue
+        annotations = getattr(base, '__annotations__', {})
+        for attr in list(base.__dict__.keys()) + list(annotations.keys()):
+            if (not attr.startswith('_abc_') and attr not in (
+                    '__abstractmethods__', '__annotations__', '__weakref__',
+                    '_is_protocol', '_is_runtime_protocol', '__dict__',
+                    '__args__', '__slots__',
+                    '__next_in_mro__', '__parameters__', '__origin__',
+                    '__orig_bases__', '__extra__', '__tree_hash__',
+                    '__doc__', '__subclasshook__', '__init__', '__new__',
+                    '__module__', '_MutableMapping__marker', '_gorg')):
+                attrs.add(attr)
+    return attrs
+
+
+def _is_callable_members_only(cls):
+    return all(callable(getattr(cls, attr, None)) for attr in _get_protocol_attrs(cls))
+
+
+# 3.8+
+if hasattr(typing, 'Protocol'):
+    Protocol = typing.Protocol
+# 3.7
+elif PEP_560:
+
+    def _no_init(self, *args, **kwargs):
+        if type(self)._is_protocol:
+            raise TypeError('Protocols cannot be instantiated')
+
+    class _ProtocolMeta(abc.ABCMeta):
+        # This metaclass is a bit unfortunate and exists only because of the lack
+        # of __instancehook__.
+        def __instancecheck__(cls, instance):
+            # We need this method for situations where attributes are
+            # assigned in __init__.
+            if ((not getattr(cls, '_is_protocol', False) or
+                 _is_callable_members_only(cls)) and
+                    issubclass(instance.__class__, cls)):
+                return True
+            if cls._is_protocol:
+                if all(hasattr(instance, attr) and
+                       (not callable(getattr(cls, attr, None)) or
+                        getattr(instance, attr) is not None)
+                       for attr in _get_protocol_attrs(cls)):
+                    return True
+            return super().__instancecheck__(instance)
+
+    class Protocol(metaclass=_ProtocolMeta):
+        # There is quite a lot of overlapping code with typing.Generic.
+        # Unfortunately it is hard to avoid this while these live in two different
+        # modules. The duplicated code will be removed when Protocol is moved to typing.
+        """Base class for protocol classes. Protocol classes are defined as::
+
+            class Proto(Protocol):
+                def meth(self) -> int:
+                    ...
+
+        Such classes are primarily used with static type checkers that recognize
+        structural subtyping (static duck-typing), for example::
+
+            class C:
+                def meth(self) -> int:
+                    return 0
+
+            def func(x: Proto) -> int:
+                return x.meth()
+
+            func(C())  # Passes static type check
+
+        See PEP 544 for details. Protocol classes decorated with
+        @typing_extensions.runtime act as simple-minded runtime protocol that checks
+        only the presence of given attributes, ignoring their type signatures.
+
+        Protocol classes can be generic, they are defined as::
+
+            class GenProto(Protocol[T]):
+                def meth(self) -> T:
+                    ...
+        """
+        __slots__ = ()
+        _is_protocol = True
+
+        def __new__(cls, *args, **kwds):
+            if cls is Protocol:
+                raise TypeError("Type Protocol cannot be instantiated; "
+                                "it can only be used as a base class")
+            return super().__new__(cls)
+
+        @typing._tp_cache
+        def __class_getitem__(cls, params):
+            if not isinstance(params, tuple):
+                params = (params,)
+            if not params and cls is not typing.Tuple:
+                raise TypeError(
+                    f"Parameter list to {cls.__qualname__}[...] cannot be empty")
+            msg = "Parameters to generic types must be types."
+            params = tuple(typing._type_check(p, msg) for p in params)  # noqa
+            if cls is Protocol:
+                # Generic can only be subscripted with unique type variables.
+                if not all(isinstance(p, typing.TypeVar) for p in params):
+                    i = 0
+                    while isinstance(params[i], typing.TypeVar):
+                        i += 1
+                    raise TypeError(
+                        "Parameters to Protocol[...] must all be type variables."
+                        f" Parameter {i + 1} is {params[i]}")
+                if len(set(params)) != len(params):
+                    raise TypeError(
+                        "Parameters to Protocol[...] must all be unique")
+            else:
+                # Subscripting a regular Generic subclass.
+                _check_generic(cls, params, len(cls.__parameters__))
+            return typing._GenericAlias(cls, params)
+
+        def __init_subclass__(cls, *args, **kwargs):
+            tvars = []
+            if '__orig_bases__' in cls.__dict__:
+                error = typing.Generic in cls.__orig_bases__
+            else:
+                error = typing.Generic in cls.__bases__
+            if error:
+                raise TypeError("Cannot inherit from plain Generic")
+            if '__orig_bases__' in cls.__dict__:
+                tvars = typing._collect_type_vars(cls.__orig_bases__)
+                # Look for Generic[T1, ..., Tn] or Protocol[T1, ..., Tn].
+                # If found, tvars must be a subset of it.
+                # If not found, tvars is it.
+                # Also check for and reject plain Generic,
+                # and reject multiple Generic[...] and/or Protocol[...].
+                gvars = None
+                for base in cls.__orig_bases__:
+                    if (isinstance(base, typing._GenericAlias) and
+                            base.__origin__ in (typing.Generic, Protocol)):
+                        # for error messages
+                        the_base = base.__origin__.__name__
+                        if gvars is not None:
+                            raise TypeError(
+                                "Cannot inherit from Generic[...]"
+                                " and/or Protocol[...] multiple types.")
+                        gvars = base.__parameters__
+                if gvars is None:
+                    gvars = tvars
+                else:
+                    tvarset = set(tvars)
+                    gvarset = set(gvars)
+                    if not tvarset <= gvarset:
+                        s_vars = ', '.join(str(t) for t in tvars if t not in gvarset)
+                        s_args = ', '.join(str(g) for g in gvars)
+                        raise TypeError(f"Some type variables ({s_vars}) are"
+                                        f" not listed in {the_base}[{s_args}]")
+                    tvars = gvars
+            cls.__parameters__ = tuple(tvars)
+
+            # Determine if this is a protocol or a concrete subclass.
+            if not cls.__dict__.get('_is_protocol', None):
+                cls._is_protocol = any(b is Protocol for b in cls.__bases__)
+
+            # Set (or override) the protocol subclass hook.
+            def _proto_hook(other):
+                if not cls.__dict__.get('_is_protocol', None):
+                    return NotImplemented
+                if not getattr(cls, '_is_runtime_protocol', False):
+                    if sys._getframe(2).f_globals['__name__'] in ['abc', 'functools']:
+                        return NotImplemented
+                    raise TypeError("Instance and class checks can only be used with"
+                                    " @runtime protocols")
+                if not _is_callable_members_only(cls):
+                    if sys._getframe(2).f_globals['__name__'] in ['abc', 'functools']:
+                        return NotImplemented
+                    raise TypeError("Protocols with non-method members"
+                                    " don't support issubclass()")
+                if not isinstance(other, type):
+                    # Same error as for issubclass(1, int)
+                    raise TypeError('issubclass() arg 1 must be a class')
+                for attr in _get_protocol_attrs(cls):
+                    for base in other.__mro__:
+                        if attr in base.__dict__:
+                            if base.__dict__[attr] is None:
+                                return NotImplemented
+                            break
+                        annotations = getattr(base, '__annotations__', {})
+                        if (isinstance(annotations, typing.Mapping) and
+                                attr in annotations and
+                                isinstance(other, _ProtocolMeta) and
+                                other._is_protocol):
+                            break
+                    else:
+                        return NotImplemented
+                return True
+            if '__subclasshook__' not in cls.__dict__:
+                cls.__subclasshook__ = _proto_hook
+
+            # We have nothing more to do for non-protocols.
+            if not cls._is_protocol:
+                return
+
+            # Check consistency of bases.
+            for base in cls.__bases__:
+                if not (base in (object, typing.Generic) or
+                        base.__module__ == 'collections.abc' and
+                        base.__name__ in _PROTO_WHITELIST or
+                        isinstance(base, _ProtocolMeta) and base._is_protocol):
+                    raise TypeError('Protocols can only inherit from other'
+                                    f' protocols, got {repr(base)}')
+            cls.__init__ = _no_init
+# 3.6
+else:
+    from typing import _next_in_mro, _type_check  # noqa
+
+    def _no_init(self, *args, **kwargs):
+        if type(self)._is_protocol:
+            raise TypeError('Protocols cannot be instantiated')
+
+    class _ProtocolMeta(GenericMeta):
+        """Internal metaclass for Protocol.
+
+        This exists so Protocol classes can be generic without deriving
+        from Generic.
+        """
+        def __new__(cls, name, bases, namespace,
+                    tvars=None, args=None, origin=None, extra=None, orig_bases=None):
+            # This is just a version copied from GenericMeta.__new__ that
+            # includes "Protocol" special treatment. (Comments removed for brevity.)
+            assert extra is None  # Protocols should not have extra
+            if tvars is not None:
+                assert origin is not None
+                assert all(isinstance(t, typing.TypeVar) for t in tvars), tvars
+            else:
+                tvars = _type_vars(bases)
+                gvars = None
+                for base in bases:
+                    if base is typing.Generic:
+                        raise TypeError("Cannot inherit from plain Generic")
+                    if (isinstance(base, GenericMeta) and
+                            base.__origin__ in (typing.Generic, Protocol)):
+                        if gvars is not None:
+                            raise TypeError(
+                                "Cannot inherit from Generic[...] or"
+                                " Protocol[...] multiple times.")
+                        gvars = base.__parameters__
+                if gvars is None:
+                    gvars = tvars
+                else:
+                    tvarset = set(tvars)
+                    gvarset = set(gvars)
+                    if not tvarset <= gvarset:
+                        s_vars = ", ".join(str(t) for t in tvars if t not in gvarset)
+                        s_args = ", ".join(str(g) for g in gvars)
+                        cls_name = "Generic" if any(b.__origin__ is typing.Generic
+                                                    for b in bases) else "Protocol"
+                        raise TypeError(f"Some type variables ({s_vars}) are"
+                                        f" not listed in {cls_name}[{s_args}]")
+                    tvars = gvars
+
+            initial_bases = bases
+            if (extra is not None and type(extra) is abc.ABCMeta and
+                    extra not in bases):
+                bases = (extra,) + bases
+            bases = tuple(_gorg(b) if isinstance(b, GenericMeta) else b
+                          for b in bases)
+            if any(isinstance(b, GenericMeta) and b is not typing.Generic for b in bases):
+                bases = tuple(b for b in bases if b is not typing.Generic)
+            namespace.update({'__origin__': origin, '__extra__': extra})
+            self = super(GenericMeta, cls).__new__(cls, name, bases, namespace,
+                                                   _root=True)
+            super(GenericMeta, self).__setattr__('_gorg',
+                                                 self if not origin else
+                                                 _gorg(origin))
+            self.__parameters__ = tvars
+            self.__args__ = tuple(... if a is typing._TypingEllipsis else
+                                  () if a is typing._TypingEmpty else
+                                  a for a in args) if args else None
+            self.__next_in_mro__ = _next_in_mro(self)
+            if orig_bases is None:
+                self.__orig_bases__ = initial_bases
+            elif origin is not None:
+                self._abc_registry = origin._abc_registry
+                self._abc_cache = origin._abc_cache
+            if hasattr(self, '_subs_tree'):
+                self.__tree_hash__ = (hash(self._subs_tree()) if origin else
+                                      super(GenericMeta, self).__hash__())
+            return self
+
+        def __init__(cls, *args, **kwargs):
+            super().__init__(*args, **kwargs)
+            if not cls.__dict__.get('_is_protocol', None):
+                cls._is_protocol = any(b is Protocol or
+                                       isinstance(b, _ProtocolMeta) and
+                                       b.__origin__ is Protocol
+                                       for b in cls.__bases__)
+            if cls._is_protocol:
+                for base in cls.__mro__[1:]:
+                    if not (base in (object, typing.Generic) or
+                            base.__module__ == 'collections.abc' and
+                            base.__name__ in _PROTO_WHITELIST or
+                            isinstance(base, typing.TypingMeta) and base._is_protocol or
+                            isinstance(base, GenericMeta) and
+                            base.__origin__ is typing.Generic):
+                        raise TypeError(f'Protocols can only inherit from other'
+                                        f' protocols, got {repr(base)}')
+
+                cls.__init__ = _no_init
+
+            def _proto_hook(other):
+                if not cls.__dict__.get('_is_protocol', None):
+                    return NotImplemented
+                if not isinstance(other, type):
+                    # Same error as for issubclass(1, int)
+                    raise TypeError('issubclass() arg 1 must be a class')
+                for attr in _get_protocol_attrs(cls):
+                    for base in other.__mro__:
+                        if attr in base.__dict__:
+                            if base.__dict__[attr] is None:
+                                return NotImplemented
+                            break
+                        annotations = getattr(base, '__annotations__', {})
+                        if (isinstance(annotations, typing.Mapping) and
+                                attr in annotations and
+                                isinstance(other, _ProtocolMeta) and
+                                other._is_protocol):
+                            break
+                    else:
+                        return NotImplemented
+                return True
+            if '__subclasshook__' not in cls.__dict__:
+                cls.__subclasshook__ = _proto_hook
+
+        def __instancecheck__(self, instance):
+            # We need this method for situations where attributes are
+            # assigned in __init__.
+            if ((not getattr(self, '_is_protocol', False) or
+                    _is_callable_members_only(self)) and
+                    issubclass(instance.__class__, self)):
+                return True
+            if self._is_protocol:
+                if all(hasattr(instance, attr) and
+                        (not callable(getattr(self, attr, None)) or
+                         getattr(instance, attr) is not None)
+                        for attr in _get_protocol_attrs(self)):
+                    return True
+            return super(GenericMeta, self).__instancecheck__(instance)
+
+        def __subclasscheck__(self, cls):
+            if self.__origin__ is not None:
+                if sys._getframe(1).f_globals['__name__'] not in ['abc', 'functools']:
+                    raise TypeError("Parameterized generics cannot be used with class "
+                                    "or instance checks")
+                return False
+            if (self.__dict__.get('_is_protocol', None) and
+                    not self.__dict__.get('_is_runtime_protocol', None)):
+                if sys._getframe(1).f_globals['__name__'] in ['abc',
+                                                              'functools',
+                                                              'typing']:
+                    return False
+                raise TypeError("Instance and class checks can only be used with"
+                                " @runtime protocols")
+            if (self.__dict__.get('_is_runtime_protocol', None) and
+                    not _is_callable_members_only(self)):
+                if sys._getframe(1).f_globals['__name__'] in ['abc',
+                                                              'functools',
+                                                              'typing']:
+                    return super(GenericMeta, self).__subclasscheck__(cls)
+                raise TypeError("Protocols with non-method members"
+                                " don't support issubclass()")
+            return super(GenericMeta, self).__subclasscheck__(cls)
+
+        @typing._tp_cache
+        def __getitem__(self, params):
+            # We also need to copy this from GenericMeta.__getitem__ to get
+            # special treatment of "Protocol". (Comments removed for brevity.)
+            if not isinstance(params, tuple):
+                params = (params,)
+            if not params and _gorg(self) is not typing.Tuple:
+                raise TypeError(
+                    f"Parameter list to {self.__qualname__}[...] cannot be empty")
+            msg = "Parameters to generic types must be types."
+            params = tuple(_type_check(p, msg) for p in params)
+            if self in (typing.Generic, Protocol):
+                if not all(isinstance(p, typing.TypeVar) for p in params):
+                    raise TypeError(
+                        f"Parameters to {repr(self)}[...] must all be type variables")
+                if len(set(params)) != len(params):
+                    raise TypeError(
+                        f"Parameters to {repr(self)}[...] must all be unique")
+                tvars = params
+                args = params
+            elif self in (typing.Tuple, typing.Callable):
+                tvars = _type_vars(params)
+                args = params
+            elif self.__origin__ in (typing.Generic, Protocol):
+                raise TypeError(f"Cannot subscript already-subscripted {repr(self)}")
+            else:
+                _check_generic(self, params, len(self.__parameters__))
+                tvars = _type_vars(params)
+                args = params
+
+            prepend = (self,) if self.__origin__ is None else ()
+            return self.__class__(self.__name__,
+                                  prepend + self.__bases__,
+                                  _no_slots_copy(self.__dict__),
+                                  tvars=tvars,
+                                  args=args,
+                                  origin=self,
+                                  extra=self.__extra__,
+                                  orig_bases=self.__orig_bases__)
+
+    class Protocol(metaclass=_ProtocolMeta):
+        """Base class for protocol classes. Protocol classes are defined as::
+
+          class Proto(Protocol):
+              def meth(self) -> int:
+                  ...
+
+        Such classes are primarily used with static type checkers that recognize
+        structural subtyping (static duck-typing), for example::
+
+          class C:
+              def meth(self) -> int:
+                  return 0
+
+          def func(x: Proto) -> int:
+              return x.meth()
+
+          func(C())  # Passes static type check
+
+        See PEP 544 for details. Protocol classes decorated with
+        @typing_extensions.runtime act as simple-minded runtime protocol that checks
+        only the presence of given attributes, ignoring their type signatures.
+
+        Protocol classes can be generic, they are defined as::
+
+          class GenProto(Protocol[T]):
+              def meth(self) -> T:
+                  ...
+        """
+        __slots__ = ()
+        _is_protocol = True
+
+        def __new__(cls, *args, **kwds):
+            if _gorg(cls) is Protocol:
+                raise TypeError("Type Protocol cannot be instantiated; "
+                                "it can be used only as a base class")
+            return typing._generic_new(cls.__next_in_mro__, cls, *args, **kwds)
+
+
+# 3.8+
+if hasattr(typing, 'runtime_checkable'):
+    runtime_checkable = typing.runtime_checkable
+# 3.6-3.7
+else:
+    def runtime_checkable(cls):
+        """Mark a protocol class as a runtime protocol, so that it
+        can be used with isinstance() and issubclass(). Raise TypeError
+        if applied to a non-protocol class.
+
+        This allows a simple-minded structural check very similar to the
+        one-offs in collections.abc such as Hashable.
+        """
+        if not isinstance(cls, _ProtocolMeta) or not cls._is_protocol:
+            raise TypeError('@runtime_checkable can be only applied to protocol classes,'
+                            f' got {cls!r}')
+        cls._is_runtime_protocol = True
+        return cls
+
+
+# Exists for backwards compatibility.
+runtime = runtime_checkable
+
+
+# 3.8+
+if hasattr(typing, 'SupportsIndex'):
+    SupportsIndex = typing.SupportsIndex
+# 3.6-3.7
+else:
+    @runtime_checkable
+    class SupportsIndex(Protocol):
+        __slots__ = ()
+
+        @abc.abstractmethod
+        def __index__(self) -> int:
+            pass
+
+
+if hasattr(typing, "Required"):
+    # The standard library TypedDict in Python 3.8 does not store runtime information
+    # about which (if any) keys are optional.  See https://bugs.python.org/issue38834
+    # The standard library TypedDict in Python 3.9.0/1 does not honour the "total"
+    # keyword with old-style TypedDict().  See https://bugs.python.org/issue42059
+    # The standard library TypedDict below Python 3.11 does not store runtime
+    # information about optional and required keys when using Required or NotRequired.
+    TypedDict = typing.TypedDict
+    _TypedDictMeta = typing._TypedDictMeta
+    is_typeddict = typing.is_typeddict
+else:
+    def _check_fails(cls, other):
+        try:
+            if sys._getframe(1).f_globals['__name__'] not in ['abc',
+                                                              'functools',
+                                                              'typing']:
+                # Typed dicts are only for static structural subtyping.
+                raise TypeError('TypedDict does not support instance and class checks')
+        except (AttributeError, ValueError):
+            pass
+        return False
+
+    def _dict_new(*args, **kwargs):
+        if not args:
+            raise TypeError('TypedDict.__new__(): not enough arguments')
+        _, args = args[0], args[1:]  # allow the "cls" keyword be passed
+        return dict(*args, **kwargs)
+
+    _dict_new.__text_signature__ = '($cls, _typename, _fields=None, /, **kwargs)'
+
+    def _typeddict_new(*args, total=True, **kwargs):
+        if not args:
+            raise TypeError('TypedDict.__new__(): not enough arguments')
+        _, args = args[0], args[1:]  # allow the "cls" keyword be passed
+        if args:
+            typename, args = args[0], args[1:]  # allow the "_typename" keyword be passed
+        elif '_typename' in kwargs:
+            typename = kwargs.pop('_typename')
+            import warnings
+            warnings.warn("Passing '_typename' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        else:
+            raise TypeError("TypedDict.__new__() missing 1 required positional "
+                            "argument: '_typename'")
+        if args:
+            try:
+                fields, = args  # allow the "_fields" keyword be passed
+            except ValueError:
+                raise TypeError('TypedDict.__new__() takes from 2 to 3 '
+                                f'positional arguments but {len(args) + 2} '
+                                'were given')
+        elif '_fields' in kwargs and len(kwargs) == 1:
+            fields = kwargs.pop('_fields')
+            import warnings
+            warnings.warn("Passing '_fields' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        else:
+            fields = None
+
+        if fields is None:
+            fields = kwargs
+        elif kwargs:
+            raise TypeError("TypedDict takes either a dict or keyword arguments,"
+                            " but not both")
+
+        ns = {'__annotations__': dict(fields)}
+        try:
+            # Setting correct module is necessary to make typed dict classes pickleable.
+            ns['__module__'] = sys._getframe(1).f_globals.get('__name__', '__main__')
+        except (AttributeError, ValueError):
+            pass
+
+        return _TypedDictMeta(typename, (), ns, total=total)
+
+    _typeddict_new.__text_signature__ = ('($cls, _typename, _fields=None,'
+                                         ' /, *, total=True, **kwargs)')
+
+    class _TypedDictMeta(type):
+        def __init__(cls, name, bases, ns, total=True):
+            super().__init__(name, bases, ns)
+
+        def __new__(cls, name, bases, ns, total=True):
+            # Create new typed dict class object.
+            # This method is called directly when TypedDict is subclassed,
+            # or via _typeddict_new when TypedDict is instantiated. This way
+            # TypedDict supports all three syntaxes described in its docstring.
+            # Subclasses and instances of TypedDict return actual dictionaries
+            # via _dict_new.
+            ns['__new__'] = _typeddict_new if name == 'TypedDict' else _dict_new
+            tp_dict = super().__new__(cls, name, (dict,), ns)
+
+            annotations = {}
+            own_annotations = ns.get('__annotations__', {})
+            msg = "TypedDict('Name', {f0: t0, f1: t1, ...}); each t must be a type"
+            own_annotations = {
+                n: typing._type_check(tp, msg) for n, tp in own_annotations.items()
+            }
+            required_keys = set()
+            optional_keys = set()
+
+            for base in bases:
+                annotations.update(base.__dict__.get('__annotations__', {}))
+                required_keys.update(base.__dict__.get('__required_keys__', ()))
+                optional_keys.update(base.__dict__.get('__optional_keys__', ()))
+
+            annotations.update(own_annotations)
+            if PEP_560:
+                for annotation_key, annotation_type in own_annotations.items():
+                    annotation_origin = get_origin(annotation_type)
+                    if annotation_origin is Annotated:
+                        annotation_args = get_args(annotation_type)
+                        if annotation_args:
+                            annotation_type = annotation_args[0]
+                            annotation_origin = get_origin(annotation_type)
+
+                    if annotation_origin is Required:
+                        required_keys.add(annotation_key)
+                    elif annotation_origin is NotRequired:
+                        optional_keys.add(annotation_key)
+                    elif total:
+                        required_keys.add(annotation_key)
+                    else:
+                        optional_keys.add(annotation_key)
+            else:
+                own_annotation_keys = set(own_annotations.keys())
+                if total:
+                    required_keys.update(own_annotation_keys)
+                else:
+                    optional_keys.update(own_annotation_keys)
+
+            tp_dict.__annotations__ = annotations
+            tp_dict.__required_keys__ = frozenset(required_keys)
+            tp_dict.__optional_keys__ = frozenset(optional_keys)
+            if not hasattr(tp_dict, '__total__'):
+                tp_dict.__total__ = total
+            return tp_dict
+
+        __instancecheck__ = __subclasscheck__ = _check_fails
+
+    TypedDict = _TypedDictMeta('TypedDict', (dict,), {})
+    TypedDict.__module__ = __name__
+    TypedDict.__doc__ = \
+        """A simple typed name space. At runtime it is equivalent to a plain dict.
+
+        TypedDict creates a dictionary type that expects all of its
+        instances to have a certain set of keys, with each key
+        associated with a value of a consistent type. This expectation
+        is not checked at runtime but is only enforced by type checkers.
+        Usage::
+
+            class Point2D(TypedDict):
+                x: int
+                y: int
+                label: str
+
+            a: Point2D = {'x': 1, 'y': 2, 'label': 'good'}  # OK
+            b: Point2D = {'z': 3, 'label': 'bad'}           # Fails type check
+
+            assert Point2D(x=1, y=2, label='first') == dict(x=1, y=2, label='first')
+
+        The type info can be accessed via the Point2D.__annotations__ dict, and
+        the Point2D.__required_keys__ and Point2D.__optional_keys__ frozensets.
+        TypedDict supports two additional equivalent forms::
+
+            Point2D = TypedDict('Point2D', x=int, y=int, label=str)
+            Point2D = TypedDict('Point2D', {'x': int, 'y': int, 'label': str})
+
+        The class syntax is only supported in Python 3.6+, while two other
+        syntax forms work for Python 2.7 and 3.2+
+        """
+
+    if hasattr(typing, "_TypedDictMeta"):
+        _TYPEDDICT_TYPES = (typing._TypedDictMeta, _TypedDictMeta)
+    else:
+        _TYPEDDICT_TYPES = (_TypedDictMeta,)
+
+    def is_typeddict(tp):
+        """Check if an annotation is a TypedDict class
+
+        For example::
+            class Film(TypedDict):
+                title: str
+                year: int
+
+            is_typeddict(Film)  # => True
+            is_typeddict(Union[list, str])  # => False
+        """
+        return isinstance(tp, tuple(_TYPEDDICT_TYPES))
+
+if hasattr(typing, "Required"):
+    get_type_hints = typing.get_type_hints
+elif PEP_560:
+    import functools
+    import types
+
+    # replaces _strip_annotations()
+    def _strip_extras(t):
+        """Strips Annotated, Required and NotRequired from a given type."""
+        if isinstance(t, _AnnotatedAlias):
+            return _strip_extras(t.__origin__)
+        if hasattr(t, "__origin__") and t.__origin__ in (Required, NotRequired):
+            return _strip_extras(t.__args__[0])
+        if isinstance(t, typing._GenericAlias):
+            stripped_args = tuple(_strip_extras(a) for a in t.__args__)
+            if stripped_args == t.__args__:
+                return t
+            return t.copy_with(stripped_args)
+        if hasattr(types, "GenericAlias") and isinstance(t, types.GenericAlias):
+            stripped_args = tuple(_strip_extras(a) for a in t.__args__)
+            if stripped_args == t.__args__:
+                return t
+            return types.GenericAlias(t.__origin__, stripped_args)
+        if hasattr(types, "UnionType") and isinstance(t, types.UnionType):
+            stripped_args = tuple(_strip_extras(a) for a in t.__args__)
+            if stripped_args == t.__args__:
+                return t
+            return functools.reduce(operator.or_, stripped_args)
+
+        return t
+
+    def get_type_hints(obj, globalns=None, localns=None, include_extras=False):
+        """Return type hints for an object.
+
+        This is often the same as obj.__annotations__, but it handles
+        forward references encoded as string literals, adds Optional[t] if a
+        default value equal to None is set and recursively replaces all
+        'Annotated[T, ...]', 'Required[T]' or 'NotRequired[T]' with 'T'
+        (unless 'include_extras=True').
+
+        The argument may be a module, class, method, or function. The annotations
+        are returned as a dictionary. For classes, annotations include also
+        inherited members.
+
+        TypeError is raised if the argument is not of a type that can contain
+        annotations, and an empty dictionary is returned if no annotations are
+        present.
+
+        BEWARE -- the behavior of globalns and localns is counterintuitive
+        (unless you are familiar with how eval() and exec() work).  The
+        search order is locals first, then globals.
+
+        - If no dict arguments are passed, an attempt is made to use the
+          globals from obj (or the respective module's globals for classes),
+          and these are also used as the locals.  If the object does not appear
+          to have globals, an empty dictionary is used.
+
+        - If one dict argument is passed, it is used for both globals and
+          locals.
+
+        - If two dict arguments are passed, they specify globals and
+          locals, respectively.
+        """
+        if hasattr(typing, "Annotated"):
+            hint = typing.get_type_hints(
+                obj, globalns=globalns, localns=localns, include_extras=True
+            )
+        else:
+            hint = typing.get_type_hints(obj, globalns=globalns, localns=localns)
+        if include_extras:
+            return hint
+        return {k: _strip_extras(t) for k, t in hint.items()}
+
+
+# Python 3.9+ has PEP 593 (Annotated)
+if hasattr(typing, 'Annotated'):
+    Annotated = typing.Annotated
+    # Not exported and not a public API, but needed for get_origin() and get_args()
+    # to work.
+    _AnnotatedAlias = typing._AnnotatedAlias
+# 3.7-3.8
+elif PEP_560:
+    class _AnnotatedAlias(typing._GenericAlias, _root=True):
+        """Runtime representation of an annotated type.
+
+        At its core 'Annotated[t, dec1, dec2, ...]' is an alias for the type 't'
+        with extra annotations. The alias behaves like a normal typing alias,
+        instantiating is the same as instantiating the underlying type, binding
+        it to types is also the same.
+        """
+        def __init__(self, origin, metadata):
+            if isinstance(origin, _AnnotatedAlias):
+                metadata = origin.__metadata__ + metadata
+                origin = origin.__origin__
+            super().__init__(origin, origin)
+            self.__metadata__ = metadata
+
+        def copy_with(self, params):
+            assert len(params) == 1
+            new_type = params[0]
+            return _AnnotatedAlias(new_type, self.__metadata__)
+
+        def __repr__(self):
+            return (f"typing_extensions.Annotated[{typing._type_repr(self.__origin__)}, "
+                    f"{', '.join(repr(a) for a in self.__metadata__)}]")
+
+        def __reduce__(self):
+            return operator.getitem, (
+                Annotated, (self.__origin__,) + self.__metadata__
+            )
+
+        def __eq__(self, other):
+            if not isinstance(other, _AnnotatedAlias):
+                return NotImplemented
+            if self.__origin__ != other.__origin__:
+                return False
+            return self.__metadata__ == other.__metadata__
+
+        def __hash__(self):
+            return hash((self.__origin__, self.__metadata__))
+
+    class Annotated:
+        """Add context specific metadata to a type.
+
+        Example: Annotated[int, runtime_check.Unsigned] indicates to the
+        hypothetical runtime_check module that this type is an unsigned int.
+        Every other consumer of this type can ignore this metadata and treat
+        this type as int.
+
+        The first argument to Annotated must be a valid type (and will be in
+        the __origin__ field), the remaining arguments are kept as a tuple in
+        the __extra__ field.
+
+        Details:
+
+        - It's an error to call `Annotated` with less than two arguments.
+        - Nested Annotated are flattened::
+
+            Annotated[Annotated[T, Ann1, Ann2], Ann3] == Annotated[T, Ann1, Ann2, Ann3]
+
+        - Instantiating an annotated type is equivalent to instantiating the
+        underlying type::
+
+            Annotated[C, Ann1](5) == C(5)
+
+        - Annotated can be used as a generic type alias::
+
+            Optimized = Annotated[T, runtime.Optimize()]
+            Optimized[int] == Annotated[int, runtime.Optimize()]
+
+            OptimizedList = Annotated[List[T], runtime.Optimize()]
+            OptimizedList[int] == Annotated[List[int], runtime.Optimize()]
+        """
+
+        __slots__ = ()
+
+        def __new__(cls, *args, **kwargs):
+            raise TypeError("Type Annotated cannot be instantiated.")
+
+        @typing._tp_cache
+        def __class_getitem__(cls, params):
+            if not isinstance(params, tuple) or len(params) < 2:
+                raise TypeError("Annotated[...] should be used "
+                                "with at least two arguments (a type and an "
+                                "annotation).")
+            allowed_special_forms = (ClassVar, Final)
+            if get_origin(params[0]) in allowed_special_forms:
+                origin = params[0]
+            else:
+                msg = "Annotated[t, ...]: t must be a type."
+                origin = typing._type_check(params[0], msg)
+            metadata = tuple(params[1:])
+            return _AnnotatedAlias(origin, metadata)
+
+        def __init_subclass__(cls, *args, **kwargs):
+            raise TypeError(
+                f"Cannot subclass {cls.__module__}.Annotated"
+            )
+# 3.6
+else:
+
+    def _is_dunder(name):
+        """Returns True if name is a __dunder_variable_name__."""
+        return len(name) > 4 and name.startswith('__') and name.endswith('__')
+
+    # Prior to Python 3.7 types did not have `copy_with`. A lot of the equality
+    # checks, argument expansion etc. are done on the _subs_tre. As a result we
+    # can't provide a get_type_hints function that strips out annotations.
+
+    class AnnotatedMeta(typing.GenericMeta):
+        """Metaclass for Annotated"""
+
+        def __new__(cls, name, bases, namespace, **kwargs):
+            if any(b is not object for b in bases):
+                raise TypeError("Cannot subclass " + str(Annotated))
+            return super().__new__(cls, name, bases, namespace, **kwargs)
+
+        @property
+        def __metadata__(self):
+            return self._subs_tree()[2]
+
+        def _tree_repr(self, tree):
+            cls, origin, metadata = tree
+            if not isinstance(origin, tuple):
+                tp_repr = typing._type_repr(origin)
+            else:
+                tp_repr = origin[0]._tree_repr(origin)
+            metadata_reprs = ", ".join(repr(arg) for arg in metadata)
+            return f'{cls}[{tp_repr}, {metadata_reprs}]'
+
+        def _subs_tree(self, tvars=None, args=None):  # noqa
+            if self is Annotated:
+                return Annotated
+            res = super()._subs_tree(tvars=tvars, args=args)
+            # Flatten nested Annotated
+            if isinstance(res[1], tuple) and res[1][0] is Annotated:
+                sub_tp = res[1][1]
+                sub_annot = res[1][2]
+                return (Annotated, sub_tp, sub_annot + res[2])
+            return res
+
+        def _get_cons(self):
+            """Return the class used to create instance of this type."""
+            if self.__origin__ is None:
+                raise TypeError("Cannot get the underlying type of a "
+                                "non-specialized Annotated type.")
+            tree = self._subs_tree()
+            while isinstance(tree, tuple) and tree[0] is Annotated:
+                tree = tree[1]
+            if isinstance(tree, tuple):
+                return tree[0]
+            else:
+                return tree
+
+        @typing._tp_cache
+        def __getitem__(self, params):
+            if not isinstance(params, tuple):
+                params = (params,)
+            if self.__origin__ is not None:  # specializing an instantiated type
+                return super().__getitem__(params)
+            elif not isinstance(params, tuple) or len(params) < 2:
+                raise TypeError("Annotated[...] should be instantiated "
+                                "with at least two arguments (a type and an "
+                                "annotation).")
+            else:
+                if (
+                    isinstance(params[0], typing._TypingBase) and
+                    type(params[0]).__name__ == "_ClassVar"
+                ):
+                    tp = params[0]
+                else:
+                    msg = "Annotated[t, ...]: t must be a type."
+                    tp = typing._type_check(params[0], msg)
+                metadata = tuple(params[1:])
+            return self.__class__(
+                self.__name__,
+                self.__bases__,
+                _no_slots_copy(self.__dict__),
+                tvars=_type_vars((tp,)),
+                # Metadata is a tuple so it won't be touched by _replace_args et al.
+                args=(tp, metadata),
+                origin=self,
+            )
+
+        def __call__(self, *args, **kwargs):
+            cons = self._get_cons()
+            result = cons(*args, **kwargs)
+            try:
+                result.__orig_class__ = self
+            except AttributeError:
+                pass
+            return result
+
+        def __getattr__(self, attr):
+            # For simplicity we just don't relay all dunder names
+            if self.__origin__ is not None and not _is_dunder(attr):
+                return getattr(self._get_cons(), attr)
+            raise AttributeError(attr)
+
+        def __setattr__(self, attr, value):
+            if _is_dunder(attr) or attr.startswith('_abc_'):
+                super().__setattr__(attr, value)
+            elif self.__origin__ is None:
+                raise AttributeError(attr)
+            else:
+                setattr(self._get_cons(), attr, value)
+
+        def __instancecheck__(self, obj):
+            raise TypeError("Annotated cannot be used with isinstance().")
+
+        def __subclasscheck__(self, cls):
+            raise TypeError("Annotated cannot be used with issubclass().")
+
+    class Annotated(metaclass=AnnotatedMeta):
+        """Add context specific metadata to a type.
+
+        Example: Annotated[int, runtime_check.Unsigned] indicates to the
+        hypothetical runtime_check module that this type is an unsigned int.
+        Every other consumer of this type can ignore this metadata and treat
+        this type as int.
+
+        The first argument to Annotated must be a valid type, the remaining
+        arguments are kept as a tuple in the __metadata__ field.
+
+        Details:
+
+        - It's an error to call `Annotated` with less than two arguments.
+        - Nested Annotated are flattened::
+
+            Annotated[Annotated[T, Ann1, Ann2], Ann3] == Annotated[T, Ann1, Ann2, Ann3]
+
+        - Instantiating an annotated type is equivalent to instantiating the
+        underlying type::
+
+            Annotated[C, Ann1](5) == C(5)
+
+        - Annotated can be used as a generic type alias::
+
+            Optimized = Annotated[T, runtime.Optimize()]
+            Optimized[int] == Annotated[int, runtime.Optimize()]
+
+            OptimizedList = Annotated[List[T], runtime.Optimize()]
+            OptimizedList[int] == Annotated[List[int], runtime.Optimize()]
+        """
+
+# Python 3.8 has get_origin() and get_args() but those implementations aren't
+# Annotated-aware, so we can't use those. Python 3.9's versions don't support
+# ParamSpecArgs and ParamSpecKwargs, so only Python 3.10's versions will do.
+if sys.version_info[:2] >= (3, 10):
+    get_origin = typing.get_origin
+    get_args = typing.get_args
+# 3.7-3.9
+elif PEP_560:
+    try:
+        # 3.9+
+        from typing import _BaseGenericAlias
+    except ImportError:
+        _BaseGenericAlias = typing._GenericAlias
+    try:
+        # 3.9+
+        from typing import GenericAlias
+    except ImportError:
+        GenericAlias = typing._GenericAlias
+
+    def get_origin(tp):
+        """Get the unsubscripted version of a type.
+
+        This supports generic types, Callable, Tuple, Union, Literal, Final, ClassVar
+        and Annotated. Return None for unsupported types. Examples::
+
+            get_origin(Literal[42]) is Literal
+            get_origin(int) is None
+            get_origin(ClassVar[int]) is ClassVar
+            get_origin(Generic) is Generic
+            get_origin(Generic[T]) is Generic
+            get_origin(Union[T, int]) is Union
+            get_origin(List[Tuple[T, T]][int]) == list
+            get_origin(P.args) is P
+        """
+        if isinstance(tp, _AnnotatedAlias):
+            return Annotated
+        if isinstance(tp, (typing._GenericAlias, GenericAlias, _BaseGenericAlias,
+                           ParamSpecArgs, ParamSpecKwargs)):
+            return tp.__origin__
+        if tp is typing.Generic:
+            return typing.Generic
+        return None
+
+    def get_args(tp):
+        """Get type arguments with all substitutions performed.
+
+        For unions, basic simplifications used by Union constructor are performed.
+        Examples::
+            get_args(Dict[str, int]) == (str, int)
+            get_args(int) == ()
+            get_args(Union[int, Union[T, int], str][int]) == (int, str)
+            get_args(Union[int, Tuple[T, int]][str]) == (int, Tuple[str, int])
+            get_args(Callable[[], T][int]) == ([], int)
+        """
+        if isinstance(tp, _AnnotatedAlias):
+            return (tp.__origin__,) + tp.__metadata__
+        if isinstance(tp, (typing._GenericAlias, GenericAlias)):
+            if getattr(tp, "_special", False):
+                return ()
+            res = tp.__args__
+            if get_origin(tp) is collections.abc.Callable and res[0] is not Ellipsis:
+                res = (list(res[:-1]), res[-1])
+            return res
+        return ()
+
+
+# 3.10+
+if hasattr(typing, 'TypeAlias'):
+    TypeAlias = typing.TypeAlias
+# 3.9
+elif sys.version_info[:2] >= (3, 9):
+    class _TypeAliasForm(typing._SpecialForm, _root=True):
+        def __repr__(self):
+            return 'typing_extensions.' + self._name
+
+    @_TypeAliasForm
+    def TypeAlias(self, parameters):
+        """Special marker indicating that an assignment should
+        be recognized as a proper type alias definition by type
+        checkers.
+
+        For example::
+
+            Predicate: TypeAlias = Callable[..., bool]
+
+        It's invalid when used anywhere except as in the example above.
+        """
+        raise TypeError(f"{self} is not subscriptable")
+# 3.7-3.8
+elif sys.version_info[:2] >= (3, 7):
+    class _TypeAliasForm(typing._SpecialForm, _root=True):
+        def __repr__(self):
+            return 'typing_extensions.' + self._name
+
+    TypeAlias = _TypeAliasForm('TypeAlias',
+                               doc="""Special marker indicating that an assignment should
+                               be recognized as a proper type alias definition by type
+                               checkers.
+
+                               For example::
+
+                                   Predicate: TypeAlias = Callable[..., bool]
+
+                               It's invalid when used anywhere except as in the example
+                               above.""")
+# 3.6
+else:
+    class _TypeAliasMeta(typing.TypingMeta):
+        """Metaclass for TypeAlias"""
+
+        def __repr__(self):
+            return 'typing_extensions.TypeAlias'
+
+    class _TypeAliasBase(typing._FinalTypingBase, metaclass=_TypeAliasMeta, _root=True):
+        """Special marker indicating that an assignment should
+        be recognized as a proper type alias definition by type
+        checkers.
+
+        For example::
+
+            Predicate: TypeAlias = Callable[..., bool]
+
+        It's invalid when used anywhere except as in the example above.
+        """
+        __slots__ = ()
+
+        def __instancecheck__(self, obj):
+            raise TypeError("TypeAlias cannot be used with isinstance().")
+
+        def __subclasscheck__(self, cls):
+            raise TypeError("TypeAlias cannot be used with issubclass().")
+
+        def __repr__(self):
+            return 'typing_extensions.TypeAlias'
+
+    TypeAlias = _TypeAliasBase(_root=True)
+
+
+# Python 3.10+ has PEP 612
+if hasattr(typing, 'ParamSpecArgs'):
+    ParamSpecArgs = typing.ParamSpecArgs
+    ParamSpecKwargs = typing.ParamSpecKwargs
+# 3.6-3.9
+else:
+    class _Immutable:
+        """Mixin to indicate that object should not be copied."""
+        __slots__ = ()
+
+        def __copy__(self):
+            return self
+
+        def __deepcopy__(self, memo):
+            return self
+
+    class ParamSpecArgs(_Immutable):
+        """The args for a ParamSpec object.
+
+        Given a ParamSpec object P, P.args is an instance of ParamSpecArgs.
+
+        ParamSpecArgs objects have a reference back to their ParamSpec:
+
+        P.args.__origin__ is P
+
+        This type is meant for runtime introspection and has no special meaning to
+        static type checkers.
+        """
+        def __init__(self, origin):
+            self.__origin__ = origin
+
+        def __repr__(self):
+            return f"{self.__origin__.__name__}.args"
+
+        def __eq__(self, other):
+            if not isinstance(other, ParamSpecArgs):
+                return NotImplemented
+            return self.__origin__ == other.__origin__
+
+    class ParamSpecKwargs(_Immutable):
+        """The kwargs for a ParamSpec object.
+
+        Given a ParamSpec object P, P.kwargs is an instance of ParamSpecKwargs.
+
+        ParamSpecKwargs objects have a reference back to their ParamSpec:
+
+        P.kwargs.__origin__ is P
+
+        This type is meant for runtime introspection and has no special meaning to
+        static type checkers.
+        """
+        def __init__(self, origin):
+            self.__origin__ = origin
+
+        def __repr__(self):
+            return f"{self.__origin__.__name__}.kwargs"
+
+        def __eq__(self, other):
+            if not isinstance(other, ParamSpecKwargs):
+                return NotImplemented
+            return self.__origin__ == other.__origin__
+
+# 3.10+
+if hasattr(typing, 'ParamSpec'):
+    ParamSpec = typing.ParamSpec
+# 3.6-3.9
+else:
+
+    # Inherits from list as a workaround for Callable checks in Python < 3.9.2.
+    class ParamSpec(list):
+        """Parameter specification variable.
+
+        Usage::
+
+           P = ParamSpec('P')
+
+        Parameter specification variables exist primarily for the benefit of static
+        type checkers.  They are used to forward the parameter types of one
+        callable to another callable, a pattern commonly found in higher order
+        functions and decorators.  They are only valid when used in ``Concatenate``,
+        or s the first argument to ``Callable``. In Python 3.10 and higher,
+        they are also supported in user-defined Generics at runtime.
+        See class Generic for more information on generic types.  An
+        example for annotating a decorator::
+
+           T = TypeVar('T')
+           P = ParamSpec('P')
+
+           def add_logging(f: Callable[P, T]) -> Callable[P, T]:
+               '''A type-safe decorator to add logging to a function.'''
+               def inner(*args: P.args, **kwargs: P.kwargs) -> T:
+                   logging.info(f'{f.__name__} was called')
+                   return f(*args, **kwargs)
+               return inner
+
+           @add_logging
+           def add_two(x: float, y: float) -> float:
+               '''Add two numbers together.'''
+               return x + y
+
+        Parameter specification variables defined with covariant=True or
+        contravariant=True can be used to declare covariant or contravariant
+        generic types.  These keyword arguments are valid, but their actual semantics
+        are yet to be decided.  See PEP 612 for details.
+
+        Parameter specification variables can be introspected. e.g.:
+
+           P.__name__ == 'T'
+           P.__bound__ == None
+           P.__covariant__ == False
+           P.__contravariant__ == False
+
+        Note that only parameter specification variables defined in global scope can
+        be pickled.
+        """
+
+        # Trick Generic __parameters__.
+        __class__ = typing.TypeVar
+
+        @property
+        def args(self):
+            return ParamSpecArgs(self)
+
+        @property
+        def kwargs(self):
+            return ParamSpecKwargs(self)
+
+        def __init__(self, name, *, bound=None, covariant=False, contravariant=False):
+            super().__init__([self])
+            self.__name__ = name
+            self.__covariant__ = bool(covariant)
+            self.__contravariant__ = bool(contravariant)
+            if bound:
+                self.__bound__ = typing._type_check(bound, 'Bound must be a type.')
+            else:
+                self.__bound__ = None
+
+            # for pickling:
+            try:
+                def_mod = sys._getframe(1).f_globals.get('__name__', '__main__')
+            except (AttributeError, ValueError):
+                def_mod = None
+            if def_mod != 'typing_extensions':
+                self.__module__ = def_mod
+
+        def __repr__(self):
+            if self.__covariant__:
+                prefix = '+'
+            elif self.__contravariant__:
+                prefix = '-'
+            else:
+                prefix = '~'
+            return prefix + self.__name__
+
+        def __hash__(self):
+            return object.__hash__(self)
+
+        def __eq__(self, other):
+            return self is other
+
+        def __reduce__(self):
+            return self.__name__
+
+        # Hack to get typing._type_check to pass.
+        def __call__(self, *args, **kwargs):
+            pass
+
+        if not PEP_560:
+            # Only needed in 3.6.
+            def _get_type_vars(self, tvars):
+                if self not in tvars:
+                    tvars.append(self)
+
+
+# 3.6-3.9
+if not hasattr(typing, 'Concatenate'):
+    # Inherits from list as a workaround for Callable checks in Python < 3.9.2.
+    class _ConcatenateGenericAlias(list):
+
+        # Trick Generic into looking into this for __parameters__.
+        if PEP_560:
+            __class__ = typing._GenericAlias
+        else:
+            __class__ = typing._TypingBase
+
+        # Flag in 3.8.
+        _special = False
+        # Attribute in 3.6 and earlier.
+        _gorg = typing.Generic
+
+        def __init__(self, origin, args):
+            super().__init__(args)
+            self.__origin__ = origin
+            self.__args__ = args
+
+        def __repr__(self):
+            _type_repr = typing._type_repr
+            return (f'{_type_repr(self.__origin__)}'
+                    f'[{", ".join(_type_repr(arg) for arg in self.__args__)}]')
+
+        def __hash__(self):
+            return hash((self.__origin__, self.__args__))
+
+        # Hack to get typing._type_check to pass in Generic.
+        def __call__(self, *args, **kwargs):
+            pass
+
+        @property
+        def __parameters__(self):
+            return tuple(
+                tp for tp in self.__args__ if isinstance(tp, (typing.TypeVar, ParamSpec))
+            )
+
+        if not PEP_560:
+            # Only required in 3.6.
+            def _get_type_vars(self, tvars):
+                if self.__origin__ and self.__parameters__:
+                    typing._get_type_vars(self.__parameters__, tvars)
+
+
+# 3.6-3.9
+@typing._tp_cache
+def _concatenate_getitem(self, parameters):
+    if parameters == ():
+        raise TypeError("Cannot take a Concatenate of no types.")
+    if not isinstance(parameters, tuple):
+        parameters = (parameters,)
+    if not isinstance(parameters[-1], ParamSpec):
+        raise TypeError("The last parameter to Concatenate should be a "
+                        "ParamSpec variable.")
+    msg = "Concatenate[arg, ...]: each arg must be a type."
+    parameters = tuple(typing._type_check(p, msg) for p in parameters)
+    return _ConcatenateGenericAlias(self, parameters)
+
+
+# 3.10+
+if hasattr(typing, 'Concatenate'):
+    Concatenate = typing.Concatenate
+    _ConcatenateGenericAlias = typing._ConcatenateGenericAlias # noqa
+# 3.9
+elif sys.version_info[:2] >= (3, 9):
+    @_TypeAliasForm
+    def Concatenate(self, parameters):
+        """Used in conjunction with ``ParamSpec`` and ``Callable`` to represent a
+        higher order function which adds, removes or transforms parameters of a
+        callable.
+
+        For example::
+
+           Callable[Concatenate[int, P], int]
+
+        See PEP 612 for detailed information.
+        """
+        return _concatenate_getitem(self, parameters)
+# 3.7-8
+elif sys.version_info[:2] >= (3, 7):
+    class _ConcatenateForm(typing._SpecialForm, _root=True):
+        def __repr__(self):
+            return 'typing_extensions.' + self._name
+
+        def __getitem__(self, parameters):
+            return _concatenate_getitem(self, parameters)
+
+    Concatenate = _ConcatenateForm(
+        'Concatenate',
+        doc="""Used in conjunction with ``ParamSpec`` and ``Callable`` to represent a
+        higher order function which adds, removes or transforms parameters of a
+        callable.
+
+        For example::
+
+           Callable[Concatenate[int, P], int]
+
+        See PEP 612 for detailed information.
+        """)
+# 3.6
+else:
+    class _ConcatenateAliasMeta(typing.TypingMeta):
+        """Metaclass for Concatenate."""
+
+        def __repr__(self):
+            return 'typing_extensions.Concatenate'
+
+    class _ConcatenateAliasBase(typing._FinalTypingBase,
+                                metaclass=_ConcatenateAliasMeta,
+                                _root=True):
+        """Used in conjunction with ``ParamSpec`` and ``Callable`` to represent a
+        higher order function which adds, removes or transforms parameters of a
+        callable.
+
+        For example::
+
+           Callable[Concatenate[int, P], int]
+
+        See PEP 612 for detailed information.
+        """
+        __slots__ = ()
+
+        def __instancecheck__(self, obj):
+            raise TypeError("Concatenate cannot be used with isinstance().")
+
+        def __subclasscheck__(self, cls):
+            raise TypeError("Concatenate cannot be used with issubclass().")
+
+        def __repr__(self):
+            return 'typing_extensions.Concatenate'
+
+        def __getitem__(self, parameters):
+            return _concatenate_getitem(self, parameters)
+
+    Concatenate = _ConcatenateAliasBase(_root=True)
+
+# 3.10+
+if hasattr(typing, 'TypeGuard'):
+    TypeGuard = typing.TypeGuard
+# 3.9
+elif sys.version_info[:2] >= (3, 9):
+    class _TypeGuardForm(typing._SpecialForm, _root=True):
+        def __repr__(self):
+            return 'typing_extensions.' + self._name
+
+    @_TypeGuardForm
+    def TypeGuard(self, parameters):
+        """Special typing form used to annotate the return type of a user-defined
+        type guard function.  ``TypeGuard`` only accepts a single type argument.
+        At runtime, functions marked this way should return a boolean.
+
+        ``TypeGuard`` aims to benefit *type narrowing* -- a technique used by static
+        type checkers to determine a more precise type of an expression within a
+        program's code flow.  Usually type narrowing is done by analyzing
+        conditional code flow and applying the narrowing to a block of code.  The
+        conditional expression here is sometimes referred to as a "type guard".
+
+        Sometimes it would be convenient to use a user-defined boolean function
+        as a type guard.  Such a function should use ``TypeGuard[...]`` as its
+        return type to alert static type checkers to this intention.
+
+        Using  ``-> TypeGuard`` tells the static type checker that for a given
+        function:
+
+        1. The return value is a boolean.
+        2. If the return value is ``True``, the type of its argument
+        is the type inside ``TypeGuard``.
+
+        For example::
+
+            def is_str(val: Union[str, float]):
+                # "isinstance" type guard
+                if isinstance(val, str):
+                    # Type of ``val`` is narrowed to ``str``
+                    ...
+                else:
+                    # Else, type of ``val`` is narrowed to ``float``.
+                    ...
+
+        Strict type narrowing is not enforced -- ``TypeB`` need not be a narrower
+        form of ``TypeA`` (it can even be a wider form) and this may lead to
+        type-unsafe results.  The main reason is to allow for things like
+        narrowing ``List[object]`` to ``List[str]`` even though the latter is not
+        a subtype of the former, since ``List`` is invariant.  The responsibility of
+        writing type-safe type guards is left to the user.
+
+        ``TypeGuard`` also works with type variables.  For more information, see
+        PEP 647 (User-Defined Type Guards).
+        """
+        item = typing._type_check(parameters, f'{self} accepts only single type.')
+        return typing._GenericAlias(self, (item,))
+# 3.7-3.8
+elif sys.version_info[:2] >= (3, 7):
+    class _TypeGuardForm(typing._SpecialForm, _root=True):
+
+        def __repr__(self):
+            return 'typing_extensions.' + self._name
+
+        def __getitem__(self, parameters):
+            item = typing._type_check(parameters,
+                                      f'{self._name} accepts only a single type')
+            return typing._GenericAlias(self, (item,))
+
+    TypeGuard = _TypeGuardForm(
+        'TypeGuard',
+        doc="""Special typing form used to annotate the return type of a user-defined
+        type guard function.  ``TypeGuard`` only accepts a single type argument.
+        At runtime, functions marked this way should return a boolean.
+
+        ``TypeGuard`` aims to benefit *type narrowing* -- a technique used by static
+        type checkers to determine a more precise type of an expression within a
+        program's code flow.  Usually type narrowing is done by analyzing
+        conditional code flow and applying the narrowing to a block of code.  The
+        conditional expression here is sometimes referred to as a "type guard".
+
+        Sometimes it would be convenient to use a user-defined boolean function
+        as a type guard.  Such a function should use ``TypeGuard[...]`` as its
+        return type to alert static type checkers to this intention.
+
+        Using  ``-> TypeGuard`` tells the static type checker that for a given
+        function:
+
+        1. The return value is a boolean.
+        2. If the return value is ``True``, the type of its argument
+        is the type inside ``TypeGuard``.
+
+        For example::
+
+            def is_str(val: Union[str, float]):
+                # "isinstance" type guard
+                if isinstance(val, str):
+                    # Type of ``val`` is narrowed to ``str``
+                    ...
+                else:
+                    # Else, type of ``val`` is narrowed to ``float``.
+                    ...
+
+        Strict type narrowing is not enforced -- ``TypeB`` need not be a narrower
+        form of ``TypeA`` (it can even be a wider form) and this may lead to
+        type-unsafe results.  The main reason is to allow for things like
+        narrowing ``List[object]`` to ``List[str]`` even though the latter is not
+        a subtype of the former, since ``List`` is invariant.  The responsibility of
+        writing type-safe type guards is left to the user.
+
+        ``TypeGuard`` also works with type variables.  For more information, see
+        PEP 647 (User-Defined Type Guards).
+        """)
+# 3.6
+else:
+    class _TypeGuard(typing._FinalTypingBase, _root=True):
+        """Special typing form used to annotate the return type of a user-defined
+        type guard function.  ``TypeGuard`` only accepts a single type argument.
+        At runtime, functions marked this way should return a boolean.
+
+        ``TypeGuard`` aims to benefit *type narrowing* -- a technique used by static
+        type checkers to determine a more precise type of an expression within a
+        program's code flow.  Usually type narrowing is done by analyzing
+        conditional code flow and applying the narrowing to a block of code.  The
+        conditional expression here is sometimes referred to as a "type guard".
+
+        Sometimes it would be convenient to use a user-defined boolean function
+        as a type guard.  Such a function should use ``TypeGuard[...]`` as its
+        return type to alert static type checkers to this intention.
+
+        Using  ``-> TypeGuard`` tells the static type checker that for a given
+        function:
+
+        1. The return value is a boolean.
+        2. If the return value is ``True``, the type of its argument
+        is the type inside ``TypeGuard``.
+
+        For example::
+
+            def is_str(val: Union[str, float]):
+                # "isinstance" type guard
+                if isinstance(val, str):
+                    # Type of ``val`` is narrowed to ``str``
+                    ...
+                else:
+                    # Else, type of ``val`` is narrowed to ``float``.
+                    ...
+
+        Strict type narrowing is not enforced -- ``TypeB`` need not be a narrower
+        form of ``TypeA`` (it can even be a wider form) and this may lead to
+        type-unsafe results.  The main reason is to allow for things like
+        narrowing ``List[object]`` to ``List[str]`` even though the latter is not
+        a subtype of the former, since ``List`` is invariant.  The responsibility of
+        writing type-safe type guards is left to the user.
+
+        ``TypeGuard`` also works with type variables.  For more information, see
+        PEP 647 (User-Defined Type Guards).
+        """
+
+        __slots__ = ('__type__',)
+
+        def __init__(self, tp=None, **kwds):
+            self.__type__ = tp
+
+        def __getitem__(self, item):
+            cls = type(self)
+            if self.__type__ is None:
+                return cls(typing._type_check(item,
+                           f'{cls.__name__[1:]} accepts only a single type.'),
+                           _root=True)
+            raise TypeError(f'{cls.__name__[1:]} cannot be further subscripted')
+
+        def _eval_type(self, globalns, localns):
+            new_tp = typing._eval_type(self.__type__, globalns, localns)
+            if new_tp == self.__type__:
+                return self
+            return type(self)(new_tp, _root=True)
+
+        def __repr__(self):
+            r = super().__repr__()
+            if self.__type__ is not None:
+                r += f'[{typing._type_repr(self.__type__)}]'
+            return r
+
+        def __hash__(self):
+            return hash((type(self).__name__, self.__type__))
+
+        def __eq__(self, other):
+            if not isinstance(other, _TypeGuard):
+                return NotImplemented
+            if self.__type__ is not None:
+                return self.__type__ == other.__type__
+            return self is other
+
+    TypeGuard = _TypeGuard(_root=True)
+
+
+if sys.version_info[:2] >= (3, 7):
+    # Vendored from cpython typing._SpecialFrom
+    class _SpecialForm(typing._Final, _root=True):
+        __slots__ = ('_name', '__doc__', '_getitem')
+
+        def __init__(self, getitem):
+            self._getitem = getitem
+            self._name = getitem.__name__
+            self.__doc__ = getitem.__doc__
+
+        def __getattr__(self, item):
+            if item in {'__name__', '__qualname__'}:
+                return self._name
+
+            raise AttributeError(item)
+
+        def __mro_entries__(self, bases):
+            raise TypeError(f"Cannot subclass {self!r}")
+
+        def __repr__(self):
+            return f'typing_extensions.{self._name}'
+
+        def __reduce__(self):
+            return self._name
+
+        def __call__(self, *args, **kwds):
+            raise TypeError(f"Cannot instantiate {self!r}")
+
+        def __or__(self, other):
+            return typing.Union[self, other]
+
+        def __ror__(self, other):
+            return typing.Union[other, self]
+
+        def __instancecheck__(self, obj):
+            raise TypeError(f"{self} cannot be used with isinstance()")
+
+        def __subclasscheck__(self, cls):
+            raise TypeError(f"{self} cannot be used with issubclass()")
+
+        @typing._tp_cache
+        def __getitem__(self, parameters):
+            return self._getitem(self, parameters)
+
+
+if hasattr(typing, "LiteralString"):
+    LiteralString = typing.LiteralString
+elif sys.version_info[:2] >= (3, 7):
+    @_SpecialForm
+    def LiteralString(self, params):
+        """Represents an arbitrary literal string.
+
+        Example::
+
+          from typing_extensions import LiteralString
+
+          def query(sql: LiteralString) -> ...:
+              ...
+
+          query("SELECT * FROM table")  # ok
+          query(f"SELECT * FROM {input()}")  # not ok
+
+        See PEP 675 for details.
+
+        """
+        raise TypeError(f"{self} is not subscriptable")
+else:
+    class _LiteralString(typing._FinalTypingBase, _root=True):
+        """Represents an arbitrary literal string.
+
+        Example::
+
+          from typing_extensions import LiteralString
+
+          def query(sql: LiteralString) -> ...:
+              ...
+
+          query("SELECT * FROM table")  # ok
+          query(f"SELECT * FROM {input()}")  # not ok
+
+        See PEP 675 for details.
+
+        """
+
+        __slots__ = ()
+
+        def __instancecheck__(self, obj):
+            raise TypeError(f"{self} cannot be used with isinstance().")
+
+        def __subclasscheck__(self, cls):
+            raise TypeError(f"{self} cannot be used with issubclass().")
+
+    LiteralString = _LiteralString(_root=True)
+
+
+if hasattr(typing, "Self"):
+    Self = typing.Self
+elif sys.version_info[:2] >= (3, 7):
+    @_SpecialForm
+    def Self(self, params):
+        """Used to spell the type of "self" in classes.
+
+        Example::
+
+          from typing import Self
+
+          class ReturnsSelf:
+              def parse(self, data: bytes) -> Self:
+                  ...
+                  return self
+
+        """
+
+        raise TypeError(f"{self} is not subscriptable")
+else:
+    class _Self(typing._FinalTypingBase, _root=True):
+        """Used to spell the type of "self" in classes.
+
+        Example::
+
+          from typing import Self
+
+          class ReturnsSelf:
+              def parse(self, data: bytes) -> Self:
+                  ...
+                  return self
+
+        """
+
+        __slots__ = ()
+
+        def __instancecheck__(self, obj):
+            raise TypeError(f"{self} cannot be used with isinstance().")
+
+        def __subclasscheck__(self, cls):
+            raise TypeError(f"{self} cannot be used with issubclass().")
+
+    Self = _Self(_root=True)
+
+
+if hasattr(typing, "Never"):
+    Never = typing.Never
+elif sys.version_info[:2] >= (3, 7):
+    @_SpecialForm
+    def Never(self, params):
+        """The bottom type, a type that has no members.
+
+        This can be used to define a function that should never be
+        called, or a function that never returns::
+
+            from typing_extensions import Never
+
+            def never_call_me(arg: Never) -> None:
+                pass
+
+            def int_or_str(arg: int | str) -> None:
+                never_call_me(arg)  # type checker error
+                match arg:
+                    case int():
+                        print("It's an int")
+                    case str():
+                        print("It's a str")
+                    case _:
+                        never_call_me(arg)  # ok, arg is of type Never
+
+        """
+
+        raise TypeError(f"{self} is not subscriptable")
+else:
+    class _Never(typing._FinalTypingBase, _root=True):
+        """The bottom type, a type that has no members.
+
+        This can be used to define a function that should never be
+        called, or a function that never returns::
+
+            from typing_extensions import Never
+
+            def never_call_me(arg: Never) -> None:
+                pass
+
+            def int_or_str(arg: int | str) -> None:
+                never_call_me(arg)  # type checker error
+                match arg:
+                    case int():
+                        print("It's an int")
+                    case str():
+                        print("It's a str")
+                    case _:
+                        never_call_me(arg)  # ok, arg is of type Never
+
+        """
+
+        __slots__ = ()
+
+        def __instancecheck__(self, obj):
+            raise TypeError(f"{self} cannot be used with isinstance().")
+
+        def __subclasscheck__(self, cls):
+            raise TypeError(f"{self} cannot be used with issubclass().")
+
+    Never = _Never(_root=True)
+
+
+if hasattr(typing, 'Required'):
+    Required = typing.Required
+    NotRequired = typing.NotRequired
+elif sys.version_info[:2] >= (3, 9):
+    class _ExtensionsSpecialForm(typing._SpecialForm, _root=True):
+        def __repr__(self):
+            return 'typing_extensions.' + self._name
+
+    @_ExtensionsSpecialForm
+    def Required(self, parameters):
+        """A special typing construct to mark a key of a total=False TypedDict
+        as required. For example:
+
+            class Movie(TypedDict, total=False):
+                title: Required[str]
+                year: int
+
+            m = Movie(
+                title='The Matrix',  # typechecker error if key is omitted
+                year=1999,
+            )
+
+        There is no runtime checking that a required key is actually provided
+        when instantiating a related TypedDict.
+        """
+        item = typing._type_check(parameters, f'{self._name} accepts only single type')
+        return typing._GenericAlias(self, (item,))
+
+    @_ExtensionsSpecialForm
+    def NotRequired(self, parameters):
+        """A special typing construct to mark a key of a TypedDict as
+        potentially missing. For example:
+
+            class Movie(TypedDict):
+                title: str
+                year: NotRequired[int]
+
+            m = Movie(
+                title='The Matrix',  # typechecker error if key is omitted
+                year=1999,
+            )
+        """
+        item = typing._type_check(parameters, f'{self._name} accepts only single type')
+        return typing._GenericAlias(self, (item,))
+
+elif sys.version_info[:2] >= (3, 7):
+    class _RequiredForm(typing._SpecialForm, _root=True):
+        def __repr__(self):
+            return 'typing_extensions.' + self._name
+
+        def __getitem__(self, parameters):
+            item = typing._type_check(parameters,
+                                      '{} accepts only single type'.format(self._name))
+            return typing._GenericAlias(self, (item,))
+
+    Required = _RequiredForm(
+        'Required',
+        doc="""A special typing construct to mark a key of a total=False TypedDict
+        as required. For example:
+
+            class Movie(TypedDict, total=False):
+                title: Required[str]
+                year: int
+
+            m = Movie(
+                title='The Matrix',  # typechecker error if key is omitted
+                year=1999,
+            )
+
+        There is no runtime checking that a required key is actually provided
+        when instantiating a related TypedDict.
+        """)
+    NotRequired = _RequiredForm(
+        'NotRequired',
+        doc="""A special typing construct to mark a key of a TypedDict as
+        potentially missing. For example:
+
+            class Movie(TypedDict):
+                title: str
+                year: NotRequired[int]
+
+            m = Movie(
+                title='The Matrix',  # typechecker error if key is omitted
+                year=1999,
+            )
+        """)
+else:
+    # NOTE: Modeled after _Final's implementation when _FinalTypingBase available
+    class _MaybeRequired(typing._FinalTypingBase, _root=True):
+        __slots__ = ('__type__',)
+
+        def __init__(self, tp=None, **kwds):
+            self.__type__ = tp
+
+        def __getitem__(self, item):
+            cls = type(self)
+            if self.__type__ is None:
+                return cls(typing._type_check(item,
+                           '{} accepts only single type.'.format(cls.__name__[1:])),
+                           _root=True)
+            raise TypeError('{} cannot be further subscripted'
+                            .format(cls.__name__[1:]))
+
+        def _eval_type(self, globalns, localns):
+            new_tp = typing._eval_type(self.__type__, globalns, localns)
+            if new_tp == self.__type__:
+                return self
+            return type(self)(new_tp, _root=True)
+
+        def __repr__(self):
+            r = super().__repr__()
+            if self.__type__ is not None:
+                r += '[{}]'.format(typing._type_repr(self.__type__))
+            return r
+
+        def __hash__(self):
+            return hash((type(self).__name__, self.__type__))
+
+        def __eq__(self, other):
+            if not isinstance(other, type(self)):
+                return NotImplemented
+            if self.__type__ is not None:
+                return self.__type__ == other.__type__
+            return self is other
+
+    class _Required(_MaybeRequired, _root=True):
+        """A special typing construct to mark a key of a total=False TypedDict
+        as required. For example:
+
+            class Movie(TypedDict, total=False):
+                title: Required[str]
+                year: int
+
+            m = Movie(
+                title='The Matrix',  # typechecker error if key is omitted
+                year=1999,
+            )
+
+        There is no runtime checking that a required key is actually provided
+        when instantiating a related TypedDict.
+        """
+
+    class _NotRequired(_MaybeRequired, _root=True):
+        """A special typing construct to mark a key of a TypedDict as
+        potentially missing. For example:
+
+            class Movie(TypedDict):
+                title: str
+                year: NotRequired[int]
+
+            m = Movie(
+                title='The Matrix',  # typechecker error if key is omitted
+                year=1999,
+            )
+        """
+
+    Required = _Required(_root=True)
+    NotRequired = _NotRequired(_root=True)
+
+
+if sys.version_info[:2] >= (3, 9):
+    class _UnpackSpecialForm(typing._SpecialForm, _root=True):
+        def __repr__(self):
+            return 'typing_extensions.' + self._name
+
+    class _UnpackAlias(typing._GenericAlias, _root=True):
+        __class__ = typing.TypeVar
+
+    @_UnpackSpecialForm
+    def Unpack(self, parameters):
+        """A special typing construct to unpack a variadic type. For example:
+
+            Shape = TypeVarTuple('Shape')
+            Batch = NewType('Batch', int)
+
+            def add_batch_axis(
+                x: Array[Unpack[Shape]]
+            ) -> Array[Batch, Unpack[Shape]]: ...
+
+        """
+        item = typing._type_check(parameters, f'{self._name} accepts only single type')
+        return _UnpackAlias(self, (item,))
+
+    def _is_unpack(obj):
+        return isinstance(obj, _UnpackAlias)
+
+elif sys.version_info[:2] >= (3, 7):
+    class _UnpackAlias(typing._GenericAlias, _root=True):
+        __class__ = typing.TypeVar
+
+    class _UnpackForm(typing._SpecialForm, _root=True):
+        def __repr__(self):
+            return 'typing_extensions.' + self._name
+
+        def __getitem__(self, parameters):
+            item = typing._type_check(parameters,
+                                      f'{self._name} accepts only single type')
+            return _UnpackAlias(self, (item,))
+
+    Unpack = _UnpackForm(
+        'Unpack',
+        doc="""A special typing construct to unpack a variadic type. For example:
+
+            Shape = TypeVarTuple('Shape')
+            Batch = NewType('Batch', int)
+
+            def add_batch_axis(
+                x: Array[Unpack[Shape]]
+            ) -> Array[Batch, Unpack[Shape]]: ...
+
+        """)
+
+    def _is_unpack(obj):
+        return isinstance(obj, _UnpackAlias)
+
+else:
+    # NOTE: Modeled after _Final's implementation when _FinalTypingBase available
+    class _Unpack(typing._FinalTypingBase, _root=True):
+        """A special typing construct to unpack a variadic type. For example:
+
+            Shape = TypeVarTuple('Shape')
+            Batch = NewType('Batch', int)
+
+            def add_batch_axis(
+                x: Array[Unpack[Shape]]
+            ) -> Array[Batch, Unpack[Shape]]: ...
+
+        """
+        __slots__ = ('__type__',)
+        __class__ = typing.TypeVar
+
+        def __init__(self, tp=None, **kwds):
+            self.__type__ = tp
+
+        def __getitem__(self, item):
+            cls = type(self)
+            if self.__type__ is None:
+                return cls(typing._type_check(item,
+                           'Unpack accepts only single type.'),
+                           _root=True)
+            raise TypeError('Unpack cannot be further subscripted')
+
+        def _eval_type(self, globalns, localns):
+            new_tp = typing._eval_type(self.__type__, globalns, localns)
+            if new_tp == self.__type__:
+                return self
+            return type(self)(new_tp, _root=True)
+
+        def __repr__(self):
+            r = super().__repr__()
+            if self.__type__ is not None:
+                r += '[{}]'.format(typing._type_repr(self.__type__))
+            return r
+
+        def __hash__(self):
+            return hash((type(self).__name__, self.__type__))
+
+        def __eq__(self, other):
+            if not isinstance(other, _Unpack):
+                return NotImplemented
+            if self.__type__ is not None:
+                return self.__type__ == other.__type__
+            return self is other
+
+        # For 3.6 only
+        def _get_type_vars(self, tvars):
+            self.__type__._get_type_vars(tvars)
+
+    Unpack = _Unpack(_root=True)
+
+    def _is_unpack(obj):
+        return isinstance(obj, _Unpack)
+
+
+class TypeVarTuple:
+    """Type variable tuple.
+
+    Usage::
+
+        Ts = TypeVarTuple('Ts')
+
+    In the same way that a normal type variable is a stand-in for a single
+    type such as ``int``, a type variable *tuple* is a stand-in for a *tuple* type such as
+    ``Tuple[int, str]``.
+
+    Type variable tuples can be used in ``Generic`` declarations.
+    Consider the following example::
+
+        class Array(Generic[*Ts]): ...
+
+    The ``Ts`` type variable tuple here behaves like ``tuple[T1, T2]``,
+    where ``T1`` and ``T2`` are type variables. To use these type variables
+    as type parameters of ``Array``, we must *unpack* the type variable tuple using
+    the star operator: ``*Ts``. The signature of ``Array`` then behaves
+    as if we had simply written ``class Array(Generic[T1, T2]): ...``.
+    In contrast to ``Generic[T1, T2]``, however, ``Generic[*Shape]`` allows
+    us to parameterise the class with an *arbitrary* number of type parameters.
+
+    Type variable tuples can be used anywhere a normal ``TypeVar`` can.
+    This includes class definitions, as shown above, as well as function
+    signatures and variable annotations::
+
+        class Array(Generic[*Ts]):
+
+            def __init__(self, shape: Tuple[*Ts]):
+                self._shape: Tuple[*Ts] = shape
+
+            def get_shape(self) -> Tuple[*Ts]:
+                return self._shape
+
+        shape = (Height(480), Width(640))
+        x: Array[Height, Width] = Array(shape)
+        y = abs(x)  # Inferred type is Array[Height, Width]
+        z = x + x   #        ...    is Array[Height, Width]
+        x.get_shape()  #     ...    is tuple[Height, Width]
+
+    """
+
+    # Trick Generic __parameters__.
+    __class__ = typing.TypeVar
+
+    def __iter__(self):
+        yield self.__unpacked__
+
+    def __init__(self, name):
+        self.__name__ = name
+
+        # for pickling:
+        try:
+            def_mod = sys._getframe(1).f_globals.get('__name__', '__main__')
+        except (AttributeError, ValueError):
+            def_mod = None
+        if def_mod != 'typing_extensions':
+            self.__module__ = def_mod
+
+        self.__unpacked__ = Unpack[self]
+
+    def __repr__(self):
+        return self.__name__
+
+    def __hash__(self):
+        return object.__hash__(self)
+
+    def __eq__(self, other):
+        return self is other
+
+    def __reduce__(self):
+        return self.__name__
+
+    def __init_subclass__(self, *args, **kwds):
+        if '_root' not in kwds:
+            raise TypeError("Cannot subclass special typing classes")
+
+    if not PEP_560:
+        # Only needed in 3.6.
+        def _get_type_vars(self, tvars):
+            if self not in tvars:
+                tvars.append(self)
+
+
+if hasattr(typing, "reveal_type"):
+    reveal_type = typing.reveal_type
+else:
+    def reveal_type(__obj: T) -> T:
+        """Reveal the inferred type of a variable.
+
+        When a static type checker encounters a call to ``reveal_type()``,
+        it will emit the inferred type of the argument::
+
+            x: int = 1
+            reveal_type(x)
+
+        Running a static type checker (e.g., ``mypy``) on this example
+        will produce output similar to 'Revealed type is "builtins.int"'.
+
+        At runtime, the function prints the runtime type of the
+        argument and returns it unchanged.
+
+        """
+        print(f"Runtime type is {type(__obj).__name__!r}", file=sys.stderr)
+        return __obj
+
+
+if hasattr(typing, "assert_never"):
+    assert_never = typing.assert_never
+else:
+    def assert_never(__arg: Never) -> Never:
+        """Assert to the type checker that a line of code is unreachable.
+
+        Example::
+
+            def int_or_str(arg: int | str) -> None:
+                match arg:
+                    case int():
+                        print("It's an int")
+                    case str():
+                        print("It's a str")
+                    case _:
+                        assert_never(arg)
+
+        If a type checker finds that a call to assert_never() is
+        reachable, it will emit an error.
+
+        At runtime, this throws an exception when called.
+
+        """
+        raise AssertionError("Expected code to be unreachable")
+
+
+if hasattr(typing, 'dataclass_transform'):
+    dataclass_transform = typing.dataclass_transform
+else:
+    def dataclass_transform(
+        *,
+        eq_default: bool = True,
+        order_default: bool = False,
+        kw_only_default: bool = False,
+        field_descriptors: typing.Tuple[
+            typing.Union[typing.Type[typing.Any], typing.Callable[..., typing.Any]],
+            ...
+        ] = (),
+    ) -> typing.Callable[[T], T]:
+        """Decorator that marks a function, class, or metaclass as providing
+        dataclass-like behavior.
+
+        Example:
+
+            from typing_extensions import dataclass_transform
+
+            _T = TypeVar("_T")
+
+            # Used on a decorator function
+            @dataclass_transform()
+            def create_model(cls: type[_T]) -> type[_T]:
+                ...
+                return cls
+
+            @create_model
+            class CustomerModel:
+                id: int
+                name: str
+
+            # Used on a base class
+            @dataclass_transform()
+            class ModelBase: ...
+
+            class CustomerModel(ModelBase):
+                id: int
+                name: str
+
+            # Used on a metaclass
+            @dataclass_transform()
+            class ModelMeta(type): ...
+
+            class ModelBase(metaclass=ModelMeta): ...
+
+            class CustomerModel(ModelBase):
+                id: int
+                name: str
+
+        Each of the ``CustomerModel`` classes defined in this example will now
+        behave similarly to a dataclass created with the ``@dataclasses.dataclass``
+        decorator. For example, the type checker will synthesize an ``__init__``
+        method.
+
+        The arguments to this decorator can be used to customize this behavior:
+        - ``eq_default`` indicates whether the ``eq`` parameter is assumed to be
+          True or False if it is omitted by the caller.
+        - ``order_default`` indicates whether the ``order`` parameter is
+          assumed to be True or False if it is omitted by the caller.
+        - ``kw_only_default`` indicates whether the ``kw_only`` parameter is
+          assumed to be True or False if it is omitted by the caller.
+        - ``field_descriptors`` specifies a static list of supported classes
+          or functions, that describe fields, similar to ``dataclasses.field()``.
+
+        At runtime, this decorator records its arguments in the
+        ``__dataclass_transform__`` attribute on the decorated object.
+
+        See PEP 681 for details.
+
+        """
+        def decorator(cls_or_fn):
+            cls_or_fn.__dataclass_transform__ = {
+                "eq_default": eq_default,
+                "order_default": order_default,
+                "kw_only_default": kw_only_default,
+                "field_descriptors": field_descriptors,
+            }
+            return cls_or_fn
+        return decorator
+
+# We have to do some monkey patching to deal with the dual nature of
+# Unpack/TypeVarTuple:
+# - We want Unpack to be a kind of TypeVar so it gets accepted in
+#   Generic[Unpack[Ts]]
+# - We want it to *not* be treated as a TypeVar for the purposes of
+#   counting generic parameters, so that when we subscript a generic,
+#   the runtime doesn't try to substitute the Unpack with the subscripted type.
+if not hasattr(typing, "TypeVarTuple"):
+    typing._collect_type_vars = _collect_type_vars
+    typing._check_generic = _check_generic