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