| # TODO: |
| # [done] Any |
| # [done] TypeVar (type variables) |
| # [done] T, KT, VT, AnyStr |
| # [done] Union, Optional |
| # [done] Tuple |
| # [done] Callable |
| # [done] Generic |
| # [don't] Protocol (similar to Generic, but for structural matching) |
| # All the collections ABCs (with Set renamed to AbstractSet): |
| # Hashable, Iterable, Iterator, |
| # Sized, Container, *Abstract*Set, MutableSet, Mapping, MutableMapping, |
| # MappingView, KeysView, ItemsView, ValuesView, |
| # Sequence, MutableSequence |
| # ByteString |
| # List, Dict, Set; FrozenSet? |
| # Other things from mypy's typing.py: |
| # - [done] Undefined |
| # - IO, BinaryIO, TextIO (?) |
| # - Match, Pattern (?) |
| # - [done] cast |
| # - forwardref |
| # - overload |
| # - namedtuple |
| # - [done] typevar (alias for TypeVar) |
| # Even more things from mypy's typing.py (that aren't in its __all__) |
| |
| # TODO nits: |
| # Get rid of asserts that are the caller's fault. |
| # Docstrings. |
| # Make it pep8-clean. |
| |
| import abc |
| import collections.abc |
| import inspect |
| import sys |
| import types |
| |
| |
| class TypingMeta(type): |
| """Base class for every type defined below. |
| |
| This overrides __new__() to require an extra keyword parameter |
| '_root', which serves as a guard against naive subclassing of the |
| typing classes. Any legitimate class defined using a metaclass |
| derived from TypingMeta (including internal subclasses created by |
| e.g. Union[X, Y]) must pass _root=True. |
| |
| This also defines a dummy constructor (all the work is done in |
| __new__) and a nicer repr(). |
| """ |
| |
| def __new__(cls, name, bases, namespace, *, _root=False): |
| if not _root: |
| raise TypeError("Cannot subclass %s" % |
| (', '.join(map(_type_repr, bases)) or '()')) |
| return super().__new__(cls, name, bases, namespace) |
| |
| def __init__(self, *args, **kwds): |
| pass |
| |
| def __repr__(self): |
| return '%s.%s' % (self.__module__, self.__qualname__) |
| |
| |
| class Final: |
| """Mix-in class to prevent instantiation.""" |
| |
| def __new__(self, *args, **kwds): |
| raise TypeError("Cannot instantiate %r" % self.__class__) |
| |
| |
| def _type_check(arg, msg): |
| """Check that the argument is a type, and return it. |
| |
| As a special case, accept None and return type(None) instead. |
| The msg argument is a human-readable error message, e.g. |
| |
| "Union[arg, ...]: arg should be a type." |
| |
| We append the repr() of the actual value (truncated to 100 chars). |
| """ |
| if arg is None: |
| return type(None) |
| if not isinstance(arg, type): |
| raise TypeError(msg + " Got %.100r." % (arg,)) |
| return arg |
| |
| |
| def _type_repr(obj): |
| """Return the repr() of an object, special-casing types. |
| |
| If obj is a type, we return a shorter version than the default |
| type.__repr__, based on the module and qualified name, which is |
| typically enough to uniquely identify a type. For everything |
| else, we fall back on repr(obj). |
| """ |
| if isinstance(obj, type) and not isinstance(obj, TypingMeta): |
| if obj.__module__ == 'builtins': |
| return obj.__qualname__ |
| else: |
| return '%s.%s' % (obj.__module__, obj.__qualname__) |
| else: |
| return repr(obj) |
| |
| |
| class AnyMeta(TypingMeta): |
| """Metaclass for Any.""" |
| |
| def __new__(cls, name, bases, namespace, _root=False): |
| self = super().__new__(cls, name, bases, namespace, _root=_root) |
| return self |
| |
| def __instancecheck__(self, instance): |
| return True |
| |
| def __subclasscheck__(self, cls): |
| if not isinstance(cls, type): |
| return super().__subclasscheck__(cls) # To TypeError. |
| return True |
| |
| |
| class Any(Final, metaclass=AnyMeta, _root=True): |
| """Special type indicating an unconstrained type. |
| |
| - Any object is an instance of Any. |
| - Any class is a subclass of Any. |
| - As a special case, Any and object are subclasses of each other. |
| """ |
| |
| |
| class TypeVar(TypingMeta, metaclass=TypingMeta, _root=True): |
| """Type variable. |
| |
| Usage:: |
| |
| T1 = TypeVar('T1') # Unconstrained |
| T2 = TypeVar('T2', t1, t2, ...) # Constrained to any of (t1, t2, ...) |
| |
| For an unconstrained type variable T, isinstance(x, T) is false |
| for all x, and similar for issubclass(cls, T). Example:: |
| |
| T = TypeVar('T') |
| assert not isinstance(42, T) |
| assert not issubclass(int, T) |
| |
| For a constrained type variable T, isinstance(x, T) is true for |
| any x that is an instance of at least one of T's constraints, |
| and similar for issubclass(cls, T). Example:: |
| |
| AnyStr = TypeVar('AnyStr', str, bytes) |
| # AnyStr behaves similar to Union[str, bytes] (but not exactly!) |
| assert not isinstance(42, AnyStr) |
| assert isinstance('', AnyStr) |
| assert isinstance(b'', AnyStr) |
| assert not issubclass(int, AnyStr) |
| assert issubclass(str, AnyStr) |
| assert issubclass(bytes, AnyStr) |
| |
| Type variables that are distinct objects are never equal (even if |
| created with the same parameters). |
| |
| You can temporarily *bind* a type variable to a specific type by |
| calling its bind() method and using the result as a context |
| manager (i.e., in a with-statement). Example:: |
| |
| with T.bind(int): |
| # In this block, T is nearly an alias for int. |
| assert isinstance(42, T) |
| assert issubclass(int, T) |
| |
| There is still a difference between T and int; issubclass(T, int) |
| is False. However, issubclass(int, T) is true. |
| |
| Binding a constrained type variable will replace the binding type |
| with the most derived of its constraints that matches. Example:: |
| |
| class MyStr(str): |
| pass |
| |
| with AnyStr.bind(MyStr): |
| # In this block, AnyStr is an alias for str, not for MyStr. |
| assert isinstance('', AnyStr) |
| assert issubclass(str, AnyStr) |
| assert not isinstance(b'', AnyStr) |
| assert not issubclass(bytes, AnyStr) |
| |
| """ |
| |
| def __new__(cls, name, *constraints): |
| self = super().__new__(cls, name, (Final,), {}, _root=True) |
| msg = "TypeVar(name, constraint, ...): constraints must be types." |
| self.__constraints__ = tuple(_type_check(t, msg) for t in constraints) |
| self.__binding__ = None |
| return self |
| |
| def __repr__(self): |
| return '~' + self.__name__ |
| |
| def __instancecheck__(self, instance): |
| if self.__binding__ is not None: |
| return isinstance(instance, self.__binding__) |
| elif not self.__constraints__: |
| return False |
| else: |
| return isinstance(instance, Union[self.__constraints__]) |
| |
| def __subclasscheck__(self, cls): |
| if cls is self: |
| return True |
| elif self.__binding__ is not None: |
| return issubclass(cls, self.__binding__) |
| elif not self.__constraints__: |
| return False |
| else: |
| return issubclass(cls, Union[self.__constraints__]) |
| |
| def bind(self, binding): |
| binding = _type_check(binding, "TypeVar.bind(t): t must be a type.") |
| if self.__constraints__: |
| best = None |
| for t in self.__constraints__: |
| if (issubclass(binding, t) and |
| (best is None or issubclass(t, best))): |
| best = t |
| if best is None: |
| raise TypeError( |
| "TypeVar.bind(t): t must match one of the constraints.") |
| binding = best |
| return VarBinding(self, binding) |
| |
| def _bind(self, binding): |
| old_binding = self.__binding__ |
| self.__binding__ = binding |
| return old_binding |
| |
| def _unbind(self, binding, old_binding): |
| assert self.__binding__ is binding, (self.__binding__, |
| binding, old_binding) |
| self.__binding__ = old_binding |
| |
| |
| # Compatibility for for mypy's typevar(). |
| def typevar(name, values=()): |
| return TypeVar(name, *values) |
| |
| |
| class VarBinding: |
| """TypeVariable binding returned by TypeVar.bind().""" |
| |
| # TODO: This is not thread-safe. We could solve this in one of |
| # two ways: by using a lock or by using thread-local state. But |
| # either of these feels overly heavy, and still doesn't work |
| # e.g. in an asyncio Task. |
| |
| def __init__(self, var, binding): |
| assert isinstance(var, TypeVar), (var, binding) |
| assert isinstance(binding, type), (var, binding) |
| self._var = var |
| self._binding = binding |
| self._old_binding = None |
| self._entered = False |
| |
| def __enter__(self): |
| if self._entered: |
| # This checks for the following scenario: |
| # bv = T.bind(<some_type>) |
| # with bv: |
| # with bv: # Will raise here. |
| # ... |
| # However, the following scenario is OK (if somewhat odd): |
| # bv = T.bind(<some_type>) |
| # with bv: |
| # ... |
| # with bv: |
| # ... |
| # The following scenario is also fine: |
| # with T.bind(<some_type>): |
| # with T.bind(<some_other_type>): |
| # ... |
| raise TypeError("Cannot reuse variable binding recursively.") |
| self._old_binding = self._var._bind(self._binding) |
| self._entered = True |
| |
| def __exit__(self, *args): |
| try: |
| self._var._unbind(self._binding, self._old_binding) |
| finally: |
| self._entered = False |
| self._old_binding = None |
| |
| |
| # Some unconstrained type variables. These are used by the container types. |
| T = TypeVar('T') # Any type. |
| KT = TypeVar('KT') # Key type. |
| VT = TypeVar('VT') # Value type. |
| |
| # A useful type variable with constraints. This represents string types. |
| # TODO: What about bytearray, memoryview? |
| AnyStr = TypeVar('AnyStr', bytes, str) |
| |
| |
| class UnionMeta(TypingMeta): |
| """Metaclass for Union.""" |
| |
| def __new__(cls, name, bases, namespace, parameters=None, _root=False): |
| if parameters is None: |
| return super().__new__(cls, name, bases, namespace, _root=_root) |
| if not isinstance(parameters, tuple): |
| raise TypeError("Expected parameters=<tuple>") |
| # Flatten out Union[Union[...], ...] and type-check non-Union args. |
| params = [] |
| msg = "Union[arg, ...]: each arg must be a type." |
| for p in parameters: |
| if isinstance(p, UnionMeta): |
| params.extend(p.__union_params__) |
| else: |
| params.append(_type_check(p, msg)) |
| # Weed out strict duplicates, preserving the first of each occurrence. |
| all_params = set(params) |
| if len(all_params) < len(params): |
| new_params = [] |
| for t in params: |
| if t in all_params: |
| new_params.append(t) |
| all_params.remove(t) |
| params = new_params |
| assert not all_params, all_params |
| # Weed out subclasses. |
| # E.g. Union[int, Employee, Manager] == Union[int, Employee]. |
| # If Any or object is present it will be the sole survivor. |
| # If both Any and object are present, Any wins. |
| all_params = set(params) |
| for t1 in params: |
| if t1 is Any: |
| return Any |
| if any(issubclass(t1, t2) for t2 in all_params - {t1}): |
| all_params.remove(t1) |
| # It's not a union if there's only one type left. |
| if len(all_params) == 1: |
| return all_params.pop() |
| # Create a new class with these params. |
| self = super().__new__(cls, name, bases, namespace, _root=True) |
| self.__union_params__ = tuple(t for t in params if t in all_params) |
| self.__union_set_params__ = frozenset(self.__union_params__) |
| return self |
| |
| def __repr__(self): |
| r = super().__repr__() |
| if self.__union_params__: |
| r += '[%s]' % (', '.join(_type_repr(t) |
| for t in self.__union_params__)) |
| return r |
| |
| def __getitem__(self, parameters): |
| if self.__union_params__ is not None: |
| raise TypeError( |
| "Cannot subscript an existing Union. Use Union[u, t] instead.") |
| if parameters == (): |
| raise TypeError("Cannot take a Union of no types.") |
| if not isinstance(parameters, tuple): |
| parameters = (parameters,) |
| return self.__class__(self.__name__, self.__bases__, |
| dict(self.__dict__), parameters, _root=True) |
| |
| def __eq__(self, other): |
| if not isinstance(other, UnionMeta): |
| return NotImplemented |
| return self.__union_set_params__ == other.__union_set_params__ |
| |
| def __hash__(self): |
| return hash(self.__union_set_params__) |
| |
| def __instancecheck__(self, instance): |
| return any(isinstance(instance, t) for t in self.__union_params__) |
| |
| def __subclasscheck__(self, cls): |
| if self.__union_params__ is None: |
| return isinstance(cls, UnionMeta) |
| elif isinstance(cls, UnionMeta): |
| if cls.__union_params__ is None: |
| return False |
| return all(issubclass(c, self) for c in (cls.__union_params__)) |
| elif isinstance(cls, TypeVar): |
| if cls in self.__union_params__: |
| return True |
| if cls.__constraints__: |
| return issubclass(Union[cls.__constraints__], self) |
| return False |
| else: |
| return any(issubclass(cls, t) for t in self.__union_params__) |
| |
| |
| class Union(Final, metaclass=UnionMeta, _root=True): |
| """Union type; Union[X, Y] means either X or Y. |
| |
| To define a union, use e.g. Union[int, str]. Details: |
| |
| - The arguments must be types and there must be at least one. |
| |
| - None as an argument is a special case and is replaced by |
| type(None). |
| |
| - Unions of unions are flattened, e.g.:: |
| |
| Union[Union[int, str], float] == Union[int, str, float] |
| |
| - Unions of a single argument vanish, e.g.:: |
| |
| Union[int] == int # The constructore actually returns int |
| |
| - Redundant arguments are skipped, e.g.:: |
| |
| Union[int, str, int] == Union[int, str] |
| |
| - When comparing unions, the argument order is ignored, e.g.:: |
| |
| Union[int, str] == Union[str, int] |
| |
| - When two arguments have a subclass relationship, the least |
| derived argument is kept, e.g.:: |
| |
| class Employee: pass |
| class Manager(Employee): pass |
| Union[int, Employee, Manager] == Union[int, Employee] |
| Union[Manager, int, Employee] == Union[int, Employee] |
| Union[Employee, Manager] == Employee |
| |
| - Corollary: if Any is present it is the sole survivor, e.g.:: |
| |
| Union[int, Any] == Any |
| |
| - Similar for object:: |
| |
| Union[int, object] == object |
| |
| - To cut a tie: Union[object, Any] == Union[Any, object] == Any. |
| |
| - You cannot subclass or instantiate a union. |
| |
| - You cannot write Union[X][Y] (what would it mean?). |
| |
| - You can use Optional[X] as a shorthand for Union[X, None]. |
| """ |
| |
| # Unsubscripted Union type has params set to None. |
| __union_params__ = None |
| __union_set_params__ = None |
| |
| |
| class OptionalMeta(TypingMeta): |
| """Metaclass for Optional.""" |
| |
| def __new__(cls, name, bases, namespace, _root=False): |
| return super().__new__(cls, name, bases, namespace, _root=_root) |
| |
| def __getitem__(self, arg): |
| if not isinstance(arg, type): |
| raise TypeError("Optional[t] requires a single type.") |
| return Union[arg, type(None)] |
| |
| |
| class Optional(Final, metaclass=OptionalMeta, _root=True): |
| """Optional type. |
| |
| Optional[X] is equivalent to Union[X, type(None)]. |
| """ |
| |
| |
| class TupleMeta(TypingMeta): |
| """Metaclass for Tuple.""" |
| |
| def __new__(cls, name, bases, namespace, parameters=None, _root=False): |
| self = super().__new__(cls, name, bases, namespace, _root=_root) |
| self.__tuple_params__ = parameters |
| return self |
| |
| def __repr__(self): |
| r = super().__repr__() |
| if self.__tuple_params__ is not None: |
| r += '[%s]' % ( |
| ', '.join(_type_repr(p) for p in self.__tuple_params__)) |
| return r |
| |
| def __getitem__(self, parameters): |
| if self.__tuple_params__ is not None: |
| raise TypeError("Cannot re-parameterize %r" % (self,)) |
| if not isinstance(parameters, tuple): |
| parameters = (parameters,) |
| msg = "Class[arg, ...]: each arg must be a type." |
| parameters = tuple(_type_check(p, msg) for p in parameters) |
| return self.__class__(self.__name__, self.__bases__, |
| dict(self.__dict__), parameters, _root=True) |
| |
| def __instancecheck__(self, t): |
| if not isinstance(t, tuple): |
| return False |
| if self.__tuple_params__ is None: |
| return True |
| return (len(t) == len(self.__tuple_params__) and |
| all(isinstance(x, p) |
| for x, p in zip(t, self.__tuple_params__))) |
| |
| def __subclasscheck__(self, cls): |
| if not isinstance(cls, type): |
| return super().__subclasscheck__(cls) # To TypeError. |
| if issubclass(cls, tuple): |
| return True # Special case. |
| if not isinstance(cls, TupleMeta): |
| return super().__subclasscheck__(cls) # False. |
| if self.__tuple_params__ is None: |
| return True |
| if cls.__tuple_params__ is None: |
| return False # ??? |
| # Covariance. |
| return (len(self.__tuple_params__) == len(cls.__tuple_params__) and |
| all(issubclass(x, p) |
| for x, p in zip(cls.__tuple_params__, |
| self.__tuple_params__))) |
| |
| |
| class Tuple(Final, metaclass=TupleMeta, _root=True): |
| """Tuple type; Tuple[X, Y] is the cross-product type of X and Y. |
| |
| Example: Tuple[T1, T2] is a tuple of two elements corresponding |
| to type variables T1 and T2. Tuple[int, float, str] is a tuple |
| of an int, a float and a string. |
| |
| To specify a variable-length tuple of homogeneous type, use Sequence[T]. |
| """ |
| |
| |
| class CallableMeta(TypingMeta): |
| """Metaclass for Callable.""" |
| |
| def __new__(cls, name, bases, namespace, _root=False, |
| args=None, result=None): |
| if args is None and result is None: |
| pass # Must be 'class Callable'. |
| else: |
| if not isinstance(args, list): |
| TypeError("Callable[args, result]: args must be a list." + |
| " Got %.100r." % (args,)) |
| msg = "Callable[[arg, ...], result]: each arg must be a type." |
| args = tuple(_type_check(arg, msg) for arg in args) |
| msg = "Callable[args, result]: result must be a type." |
| result = _type_check(result, msg) |
| self = super().__new__(cls, name, bases, namespace, _root=_root) |
| self.__args__ = args |
| self.__result__ = result |
| return self |
| |
| def __repr__(self): |
| r = super().__repr__() |
| if self.__args__ is not None or self.__result__ is not None: |
| r += '%s[[%s], %s]' % (self.__qualname__, |
| ', '.join(_type_repr(t) |
| for t in self.__args__), |
| _type_repr(self.__result__)) |
| return r |
| |
| def __getitem__(self, parameters): |
| if self.__args__ is not None or self.__result__ is not None: |
| raise TypeError("This Callable type is already parameterized.") |
| if not isinstance(parameters, tuple) or len(parameters) != 2: |
| raise TypeError( |
| "Callable must be used as Callable[[arg, ...], result].") |
| args, result = parameters |
| return self.__class__(self.__name__, self.__bases__, |
| dict(self.__dict__), _root=True, |
| args=args, result=result) |
| |
| def __eq__(self, other): |
| if not isinstance(other, CallableMeta): |
| return NotImplemented |
| return (self.__args__ == other.__args__ and |
| self.__result__ == other.__result__) |
| |
| def __hash__(self): |
| return hash(self.__args__) ^ hash(self.__result__) |
| |
| def __instancecheck__(self, instance): |
| if not callable(instance): |
| return False |
| if self.__args__ is None and self.__result__ is None: |
| return True |
| assert self.__args__ is not None |
| assert self.__result__ is not None |
| my_args, my_result = self.__args__, self.__result__ |
| # Would it be better to use Signature objects? |
| try: |
| (args, varargs, varkw, defaults, kwonlyargs, kwonlydefaults, |
| annotations) = inspect.getfullargspec(instance) |
| except TypeError: |
| return False # We can't find the signature. Give up. |
| if kwonlyargs and (not kwonlydefaults or |
| len(kwonlydefaults) < len(kwonlyargs)): |
| return False |
| if isinstance(instance, types.MethodType): |
| # For methods, getfullargspec() includes self/cls, |
| # but it's not part of the call signature, so drop it. |
| del args[0] |
| min_call_args = len(args) |
| if defaults: |
| min_call_args -= len(defaults) |
| if varargs: |
| max_call_args = 999999999 |
| if len(args) < len(my_args): |
| args += [varargs] * (len(my_args) - len(args)) |
| else: |
| max_call_args = len(args) |
| if not min_call_args <= len(my_args) <= max_call_args: |
| return False |
| msg = ("When testing isinstance(<callable>, Callable[...], " + |
| "<calleble>'s annotations must be types.") |
| for my_arg_type, name in zip(my_args, args): |
| if name in annotations: |
| annot_type = _type_check(annotations[name], msg) |
| else: |
| annot_type = Any |
| if not issubclass(my_arg_type, annot_type): |
| return False |
| # TODO: If mutable type, check invariance? |
| if 'return' in annotations: |
| annot_return_type = _type_check(annotations['return'], msg) |
| # Note contravariance here! |
| if not issubclass(annot_return_type, my_result): |
| return False |
| # Can't find anything wrong... |
| return True |
| |
| def __subclasscheck__(self, cls): |
| # Compute issubclass(cls, self). |
| if not isinstance(cls, CallableMeta): |
| return super().__subclasscheck__(cls) |
| if self.__args__ is None and self.__result__ is None: |
| return True |
| # We're not doing covariance or contravariance -- this is *invariance*. |
| return self == cls |
| |
| |
| class Callable(Final, metaclass=CallableMeta, _root=True): |
| """Callable type; Callable[[int], str] is a function of (int) -> str. |
| |
| The subscription syntax must always be used with exactly two |
| values: the argument list and the return type. The argument list |
| must be a list of types; the return type must be a single type. |
| |
| There is no syntax to indicate optional or keyword arguments, |
| such function types are rarely used as callback types. |
| """ |
| |
| |
| class GenericMeta(TypingMeta, abc.ABCMeta): |
| """Metaclass for generic types.""" |
| |
| # TODO: Constrain more how Generic is used; only a few |
| # standard patterns should be allowed. |
| |
| # TODO: Somehow repr() of a subclass parameterized comes out with |
| # module=typing. |
| |
| def __new__(cls, name, bases, namespace, parameters=None): |
| if parameters is None: |
| # Extract parameters from direct base classes. Only |
| # direct bases are considered and only those that are |
| # themselves generic, and parameterized with type |
| # variables. Don't use bases like Any, Union, Tuple, |
| # Callable or type variables. |
| params = None |
| for base in bases: |
| if isinstance(base, TypingMeta): |
| if not isinstance(base, GenericMeta): |
| raise TypeError( |
| "You cannot inherit from magic class %s" % |
| repr(base)) |
| if base.__parameters__ is None: |
| continue |
| if params is None: |
| params = [] |
| for bp in base.__parameters__: |
| if isinstance(bp, TypingMeta): |
| if not isinstance(bp, TypeVar): |
| raise TypeError( |
| "Cannot inherit from a generic class " |
| "parameterized with a " |
| "non-type-variable %s" % bp) |
| if bp not in params: |
| params.append(bp) |
| if params is not None: |
| parameters = tuple(params) |
| |
| # Check the caller's locals to see if we're overriding a |
| # forward reference. If so, update the class in place. |
| f = sys._getframe(1) |
| if f.f_locals and name in f.f_locals: |
| overriding = f.f_locals[name] |
| if (isinstance(overriding, cls) and |
| overriding.__bases__ == bases and |
| overriding.__parameters__ == parameters): |
| self = overriding |
| for k, v in namespace.items(): |
| setattr(self, k, v) |
| return self |
| self = super().__new__(cls, name, bases, namespace, _root=True) |
| self.__parameters__ = parameters |
| return self |
| |
| def __repr__(self): |
| r = super().__repr__() |
| if self.__parameters__ is not None: |
| r += '[%s]' % ( |
| ', '.join(_type_repr(p) for p in self.__parameters__)) |
| return r |
| |
| def __eq__(self, other): |
| if not isinstance(other, GenericMeta): |
| return NotImplemented |
| return (self.__name__ == other.__name__ and |
| self.__parameters__ == other.__parameters__) |
| |
| def __hash__(self): |
| return hash((self.__name__, self.__parameters__)) |
| |
| def __getitem__(self, params): |
| if not isinstance(params, tuple): |
| params = (params,) |
| if not params: |
| raise TypeError("Cannot have empty parameter list") |
| msg = "Parameters to generic types must be types." |
| params = tuple(_type_check(p, msg) for p in params) |
| if self.__parameters__ is None: |
| for p in params: |
| if not isinstance(p, TypeVar): |
| raise TypeError("Initial parameters must be " |
| "type variables; got %s" % p) |
| else: |
| if len(params) != len(self.__parameters__): |
| raise TypeError("Cannot change parameter count from %d to %d" % |
| (len(self.__parameters__), len(params))) |
| for new, old in zip(params, self.__parameters__): |
| if isinstance(old, TypeVar) and not old.__constraints__: |
| # Substituting for an unconstrained TypeVar is always OK. |
| continue |
| if not issubclass(new, old): |
| raise TypeError( |
| "Cannot substitute %s for %s in %s" % |
| (_type_repr(new), _type_repr(old), self)) |
| return self.__class__(self.__name__, self.__bases__, |
| dict(self.__dict__), |
| parameters=params) |
| |
| |
| class Generic(metaclass=GenericMeta): |
| """Abstract base class for generic types. |
| |
| A generic type is typically declared by inheriting from an |
| instantiation of this class with one or more type variables. |
| For example, a generic mapping type might be defined as:: |
| |
| class Mapping(Generic[KT, VT]): |
| def __getitem__(self, key: KT) -> VT: |
| ... |
| # Etc. |
| |
| This class can then be used as follows:: |
| |
| def lookup_name(mapping: Mapping, key: KT, default: VT) -> VT: |
| try: |
| return mapping[key] |
| except KeyError: |
| return default |
| |
| For clarity the type variables may be redefined, e.g.:: |
| |
| X = TypeVar('X') |
| Y = TypeVar('Y') |
| def lookup_name(mapping: Mapping[X, Y], key: X, default: Y) -> Y: |
| # Same body as above. |
| """ |
| |
| |
| class Undefined: |
| """An undefined value. |
| |
| Example:: |
| |
| x = Undefined(typ) |
| |
| This tells the type checker that x has the given type but its |
| value should be considered undefined. At runtime x is an instance |
| of Undefined. The actual type can be introspected by looking at |
| x.__type__ and its str() and repr() are defined, but any other |
| operations or attributes will raise an exception. |
| """ |
| |
| __slots__ = ['__type__'] |
| |
| def __new__(cls, typ): |
| typ = _type_check(typ, "Undefined(t): t must be a type.") |
| self = super().__new__(cls) |
| self.__type__ = typ |
| return self |
| |
| __hash__ = None |
| |
| def __repr__(self): |
| return '%s(%s)' % (_type_repr(self.__class__), |
| _type_repr(self.__type__)) |
| |
| |
| def cast(typ, val): |
| """Cast a value to a type. |
| |
| This returns the value unchanged. To the type checker this |
| signals that the return value has the designated type, but at |
| runtime we intentionally don't check this. However, we do |
| insist that the first argument is a type. |
| """ |
| _type_check(typ, "cast(t, v): t must be a type.") |
| return val |
