| """ |
| ast |
| ~~~ |
| |
| The `ast` module helps Python applications to process trees of the Python |
| abstract syntax grammar. The abstract syntax itself might change with |
| each Python release; this module helps to find out programmatically what |
| the current grammar looks like and allows modifications of it. |
| |
| An abstract syntax tree can be generated by passing `ast.PyCF_ONLY_AST` as |
| a flag to the `compile()` builtin function or by using the `parse()` |
| function from this module. The result will be a tree of objects whose |
| classes all inherit from `ast.AST`. |
| |
| A modified abstract syntax tree can be compiled into a Python code object |
| using the built-in `compile()` function. |
| |
| Additionally various helper functions are provided that make working with |
| the trees simpler. The main intention of the helper functions and this |
| module in general is to provide an easy to use interface for libraries |
| that work tightly with the python syntax (template engines for example). |
| |
| |
| :copyright: Copyright 2008 by Armin Ronacher. |
| :license: Python License. |
| """ |
| from _ast import * |
| |
| |
| def parse(source, filename='<unknown>', mode='exec', *, |
| type_comments=False, feature_version=None): |
| """ |
| Parse the source into an AST node. |
| Equivalent to compile(source, filename, mode, PyCF_ONLY_AST). |
| Pass type_comments=True to get back type comments where the syntax allows. |
| """ |
| flags = PyCF_ONLY_AST |
| if type_comments: |
| flags |= PyCF_TYPE_COMMENTS |
| if isinstance(feature_version, tuple): |
| major, minor = feature_version # Should be a 2-tuple. |
| assert major == 3 |
| feature_version = minor |
| elif feature_version is None: |
| feature_version = -1 |
| # Else it should be an int giving the minor version for 3.x. |
| return compile(source, filename, mode, flags, |
| _feature_version=feature_version) |
| |
| |
| def literal_eval(node_or_string): |
| """ |
| Safely evaluate an expression node or a string containing a Python |
| expression. The string or node provided may only consist of the following |
| Python literal structures: strings, bytes, numbers, tuples, lists, dicts, |
| sets, booleans, and None. |
| """ |
| if isinstance(node_or_string, str): |
| node_or_string = parse(node_or_string, mode='eval') |
| if isinstance(node_or_string, Expression): |
| node_or_string = node_or_string.body |
| def _convert_num(node): |
| if isinstance(node, Constant): |
| if type(node.value) in (int, float, complex): |
| return node.value |
| raise ValueError('malformed node or string: ' + repr(node)) |
| def _convert_signed_num(node): |
| if isinstance(node, UnaryOp) and isinstance(node.op, (UAdd, USub)): |
| operand = _convert_num(node.operand) |
| if isinstance(node.op, UAdd): |
| return + operand |
| else: |
| return - operand |
| return _convert_num(node) |
| def _convert(node): |
| if isinstance(node, Constant): |
| return node.value |
| elif isinstance(node, Tuple): |
| return tuple(map(_convert, node.elts)) |
| elif isinstance(node, List): |
| return list(map(_convert, node.elts)) |
| elif isinstance(node, Set): |
| return set(map(_convert, node.elts)) |
| elif isinstance(node, Dict): |
| return dict(zip(map(_convert, node.keys), |
| map(_convert, node.values))) |
| elif isinstance(node, BinOp) and isinstance(node.op, (Add, Sub)): |
| left = _convert_signed_num(node.left) |
| right = _convert_num(node.right) |
| if isinstance(left, (int, float)) and isinstance(right, complex): |
| if isinstance(node.op, Add): |
| return left + right |
| else: |
| return left - right |
| return _convert_signed_num(node) |
| return _convert(node_or_string) |
| |
| |
| def dump(node, annotate_fields=True, include_attributes=False): |
| """ |
| Return a formatted dump of the tree in node. This is mainly useful for |
| debugging purposes. If annotate_fields is true (by default), |
| the returned string will show the names and the values for fields. |
| If annotate_fields is false, the result string will be more compact by |
| omitting unambiguous field names. Attributes such as line |
| numbers and column offsets are not dumped by default. If this is wanted, |
| include_attributes can be set to true. |
| """ |
| def _format(node): |
| if isinstance(node, AST): |
| args = [] |
| keywords = annotate_fields |
| for field in node._fields: |
| try: |
| value = getattr(node, field) |
| except AttributeError: |
| keywords = True |
| else: |
| if keywords: |
| args.append('%s=%s' % (field, _format(value))) |
| else: |
| args.append(_format(value)) |
| if include_attributes and node._attributes: |
| for a in node._attributes: |
| try: |
| args.append('%s=%s' % (a, _format(getattr(node, a)))) |
| except AttributeError: |
| pass |
| return '%s(%s)' % (node.__class__.__name__, ', '.join(args)) |
| elif isinstance(node, list): |
| return '[%s]' % ', '.join(_format(x) for x in node) |
| return repr(node) |
| if not isinstance(node, AST): |
| raise TypeError('expected AST, got %r' % node.__class__.__name__) |
| return _format(node) |
| |
| |
| def copy_location(new_node, old_node): |
| """ |
| Copy source location (`lineno`, `col_offset`, `end_lineno`, and `end_col_offset` |
| attributes) from *old_node* to *new_node* if possible, and return *new_node*. |
| """ |
| for attr in 'lineno', 'col_offset', 'end_lineno', 'end_col_offset': |
| if attr in old_node._attributes and attr in new_node._attributes \ |
| and hasattr(old_node, attr): |
| setattr(new_node, attr, getattr(old_node, attr)) |
| return new_node |
| |
| |
| def fix_missing_locations(node): |
| """ |
| When you compile a node tree with compile(), the compiler expects lineno and |
| col_offset attributes for every node that supports them. This is rather |
| tedious to fill in for generated nodes, so this helper adds these attributes |
| recursively where not already set, by setting them to the values of the |
| parent node. It works recursively starting at *node*. |
| """ |
| def _fix(node, lineno, col_offset, end_lineno, end_col_offset): |
| if 'lineno' in node._attributes: |
| if not hasattr(node, 'lineno'): |
| node.lineno = lineno |
| else: |
| lineno = node.lineno |
| if 'end_lineno' in node._attributes: |
| if not hasattr(node, 'end_lineno'): |
| node.end_lineno = end_lineno |
| else: |
| end_lineno = node.end_lineno |
| if 'col_offset' in node._attributes: |
| if not hasattr(node, 'col_offset'): |
| node.col_offset = col_offset |
| else: |
| col_offset = node.col_offset |
| if 'end_col_offset' in node._attributes: |
| if not hasattr(node, 'end_col_offset'): |
| node.end_col_offset = end_col_offset |
| else: |
| end_col_offset = node.end_col_offset |
| for child in iter_child_nodes(node): |
| _fix(child, lineno, col_offset, end_lineno, end_col_offset) |
| _fix(node, 1, 0, 1, 0) |
| return node |
| |
| |
| def increment_lineno(node, n=1): |
| """ |
| Increment the line number and end line number of each node in the tree |
| starting at *node* by *n*. This is useful to "move code" to a different |
| location in a file. |
| """ |
| for child in walk(node): |
| if 'lineno' in child._attributes: |
| child.lineno = getattr(child, 'lineno', 0) + n |
| if 'end_lineno' in child._attributes: |
| child.end_lineno = getattr(child, 'end_lineno', 0) + n |
| return node |
| |
| |
| def iter_fields(node): |
| """ |
| Yield a tuple of ``(fieldname, value)`` for each field in ``node._fields`` |
| that is present on *node*. |
| """ |
| for field in node._fields: |
| try: |
| yield field, getattr(node, field) |
| except AttributeError: |
| pass |
| |
| |
| def iter_child_nodes(node): |
| """ |
| Yield all direct child nodes of *node*, that is, all fields that are nodes |
| and all items of fields that are lists of nodes. |
| """ |
| for name, field in iter_fields(node): |
| if isinstance(field, AST): |
| yield field |
| elif isinstance(field, list): |
| for item in field: |
| if isinstance(item, AST): |
| yield item |
| |
| |
| def get_docstring(node, clean=True): |
| """ |
| Return the docstring for the given node or None if no docstring can |
| be found. If the node provided does not have docstrings a TypeError |
| will be raised. |
| |
| If *clean* is `True`, all tabs are expanded to spaces and any whitespace |
| that can be uniformly removed from the second line onwards is removed. |
| """ |
| if not isinstance(node, (AsyncFunctionDef, FunctionDef, ClassDef, Module)): |
| raise TypeError("%r can't have docstrings" % node.__class__.__name__) |
| if not(node.body and isinstance(node.body[0], Expr)): |
| return None |
| node = node.body[0].value |
| if isinstance(node, Str): |
| text = node.s |
| elif isinstance(node, Constant) and isinstance(node.value, str): |
| text = node.value |
| else: |
| return None |
| if clean: |
| import inspect |
| text = inspect.cleandoc(text) |
| return text |
| |
| |
| def _splitlines_no_ff(source): |
| """Split a string into lines ignoring form feed and other chars. |
| |
| This mimics how the Python parser splits source code. |
| """ |
| idx = 0 |
| lines = [] |
| next_line = '' |
| while idx < len(source): |
| c = source[idx] |
| next_line += c |
| idx += 1 |
| # Keep \r\n together |
| if c == '\r' and idx < len(source) and source[idx] == '\n': |
| next_line += '\n' |
| idx += 1 |
| if c in '\r\n': |
| lines.append(next_line) |
| next_line = '' |
| |
| if next_line: |
| lines.append(next_line) |
| return lines |
| |
| |
| def _pad_whitespace(source): |
| """Replace all chars except '\f\t' in a line with spaces.""" |
| result = '' |
| for c in source: |
| if c in '\f\t': |
| result += c |
| else: |
| result += ' ' |
| return result |
| |
| |
| def get_source_segment(source, node, *, padded=False): |
| """Get source code segment of the *source* that generated *node*. |
| |
| If some location information (`lineno`, `end_lineno`, `col_offset`, |
| or `end_col_offset`) is missing, return None. |
| |
| If *padded* is `True`, the first line of a multi-line statement will |
| be padded with spaces to match its original position. |
| """ |
| try: |
| lineno = node.lineno - 1 |
| end_lineno = node.end_lineno - 1 |
| col_offset = node.col_offset |
| end_col_offset = node.end_col_offset |
| except AttributeError: |
| return None |
| |
| lines = _splitlines_no_ff(source) |
| if end_lineno == lineno: |
| return lines[lineno].encode()[col_offset:end_col_offset].decode() |
| |
| if padded: |
| padding = _pad_whitespace(lines[lineno].encode()[:col_offset].decode()) |
| else: |
| padding = '' |
| |
| first = padding + lines[lineno].encode()[col_offset:].decode() |
| last = lines[end_lineno].encode()[:end_col_offset].decode() |
| lines = lines[lineno+1:end_lineno] |
| |
| lines.insert(0, first) |
| lines.append(last) |
| return ''.join(lines) |
| |
| |
| def walk(node): |
| """ |
| Recursively yield all descendant nodes in the tree starting at *node* |
| (including *node* itself), in no specified order. This is useful if you |
| only want to modify nodes in place and don't care about the context. |
| """ |
| from collections import deque |
| todo = deque([node]) |
| while todo: |
| node = todo.popleft() |
| todo.extend(iter_child_nodes(node)) |
| yield node |
| |
| |
| class NodeVisitor(object): |
| """ |
| A node visitor base class that walks the abstract syntax tree and calls a |
| visitor function for every node found. This function may return a value |
| which is forwarded by the `visit` method. |
| |
| This class is meant to be subclassed, with the subclass adding visitor |
| methods. |
| |
| Per default the visitor functions for the nodes are ``'visit_'`` + |
| class name of the node. So a `TryFinally` node visit function would |
| be `visit_TryFinally`. This behavior can be changed by overriding |
| the `visit` method. If no visitor function exists for a node |
| (return value `None`) the `generic_visit` visitor is used instead. |
| |
| Don't use the `NodeVisitor` if you want to apply changes to nodes during |
| traversing. For this a special visitor exists (`NodeTransformer`) that |
| allows modifications. |
| """ |
| |
| def visit(self, node): |
| """Visit a node.""" |
| method = 'visit_' + node.__class__.__name__ |
| visitor = getattr(self, method, self.generic_visit) |
| return visitor(node) |
| |
| def generic_visit(self, node): |
| """Called if no explicit visitor function exists for a node.""" |
| for field, value in iter_fields(node): |
| if isinstance(value, list): |
| for item in value: |
| if isinstance(item, AST): |
| self.visit(item) |
| elif isinstance(value, AST): |
| self.visit(value) |
| |
| def visit_Constant(self, node): |
| value = node.value |
| type_name = _const_node_type_names.get(type(value)) |
| if type_name is None: |
| for cls, name in _const_node_type_names.items(): |
| if isinstance(value, cls): |
| type_name = name |
| break |
| if type_name is not None: |
| method = 'visit_' + type_name |
| try: |
| visitor = getattr(self, method) |
| except AttributeError: |
| pass |
| else: |
| import warnings |
| warnings.warn(f"{method} is deprecated; add visit_Constant", |
| PendingDeprecationWarning, 2) |
| return visitor(node) |
| return self.generic_visit(node) |
| |
| |
| class NodeTransformer(NodeVisitor): |
| """ |
| A :class:`NodeVisitor` subclass that walks the abstract syntax tree and |
| allows modification of nodes. |
| |
| The `NodeTransformer` will walk the AST and use the return value of the |
| visitor methods to replace or remove the old node. If the return value of |
| the visitor method is ``None``, the node will be removed from its location, |
| otherwise it is replaced with the return value. The return value may be the |
| original node in which case no replacement takes place. |
| |
| Here is an example transformer that rewrites all occurrences of name lookups |
| (``foo``) to ``data['foo']``:: |
| |
| class RewriteName(NodeTransformer): |
| |
| def visit_Name(self, node): |
| return copy_location(Subscript( |
| value=Name(id='data', ctx=Load()), |
| slice=Index(value=Str(s=node.id)), |
| ctx=node.ctx |
| ), node) |
| |
| Keep in mind that if the node you're operating on has child nodes you must |
| either transform the child nodes yourself or call the :meth:`generic_visit` |
| method for the node first. |
| |
| For nodes that were part of a collection of statements (that applies to all |
| statement nodes), the visitor may also return a list of nodes rather than |
| just a single node. |
| |
| Usually you use the transformer like this:: |
| |
| node = YourTransformer().visit(node) |
| """ |
| |
| def generic_visit(self, node): |
| for field, old_value in iter_fields(node): |
| if isinstance(old_value, list): |
| new_values = [] |
| for value in old_value: |
| if isinstance(value, AST): |
| value = self.visit(value) |
| if value is None: |
| continue |
| elif not isinstance(value, AST): |
| new_values.extend(value) |
| continue |
| new_values.append(value) |
| old_value[:] = new_values |
| elif isinstance(old_value, AST): |
| new_node = self.visit(old_value) |
| if new_node is None: |
| delattr(node, field) |
| else: |
| setattr(node, field, new_node) |
| return node |
| |
| |
| # The following code is for backward compatibility. |
| # It will be removed in future. |
| |
| def _getter(self): |
| return self.value |
| |
| def _setter(self, value): |
| self.value = value |
| |
| Constant.n = property(_getter, _setter) |
| Constant.s = property(_getter, _setter) |
| |
| class _ABC(type): |
| |
| def __instancecheck__(cls, inst): |
| if not isinstance(inst, Constant): |
| return False |
| if cls in _const_types: |
| try: |
| value = inst.value |
| except AttributeError: |
| return False |
| else: |
| return ( |
| isinstance(value, _const_types[cls]) and |
| not isinstance(value, _const_types_not.get(cls, ())) |
| ) |
| return type.__instancecheck__(cls, inst) |
| |
| def _new(cls, *args, **kwargs): |
| if cls in _const_types: |
| return Constant(*args, **kwargs) |
| return Constant.__new__(cls, *args, **kwargs) |
| |
| class Num(Constant, metaclass=_ABC): |
| _fields = ('n',) |
| __new__ = _new |
| |
| class Str(Constant, metaclass=_ABC): |
| _fields = ('s',) |
| __new__ = _new |
| |
| class Bytes(Constant, metaclass=_ABC): |
| _fields = ('s',) |
| __new__ = _new |
| |
| class NameConstant(Constant, metaclass=_ABC): |
| __new__ = _new |
| |
| class Ellipsis(Constant, metaclass=_ABC): |
| _fields = () |
| |
| def __new__(cls, *args, **kwargs): |
| if cls is Ellipsis: |
| return Constant(..., *args, **kwargs) |
| return Constant.__new__(cls, *args, **kwargs) |
| |
| _const_types = { |
| Num: (int, float, complex), |
| Str: (str,), |
| Bytes: (bytes,), |
| NameConstant: (type(None), bool), |
| Ellipsis: (type(...),), |
| } |
| _const_types_not = { |
| Num: (bool,), |
| } |
| _const_node_type_names = { |
| bool: 'NameConstant', # should be before int |
| type(None): 'NameConstant', |
| int: 'Num', |
| float: 'Num', |
| complex: 'Num', |
| str: 'Str', |
| bytes: 'Bytes', |
| type(...): 'Ellipsis', |
| } |
