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ast.py
""" 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 _raise_malformed_node(node): raise ValueError(f'malformed node or string: {node!r}') def _convert_num(node): if not isinstance(node, Constant) or type(node.value) not in (int, float, complex): _raise_malformed_node(node) return node.value 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): if len(node.keys) != len(node.values): _raise_malformed_node(node) 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: value = getattr(old_node, attr, None) # end_lineno and end_col_offset are optional attributes, and they # should be copied whether the value is None or not. if value is not None or ( hasattr(old_node, attr) and attr.startswith("end_") ): setattr(new_node, attr, value) 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 and (end_lineno := getattr(child, "end_lineno", 0)) is not None ): child.end_lineno = end_lineno + 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): r"""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 Subscript( value=Name(id='data', ctx=Load()), slice=Index(value=Str(s=node.id)), ctx=node.ctx ) 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): for key in kwargs: if key not in cls._fields: # arbitrary keyword arguments are accepted continue pos = cls._fields.index(key) if pos < len(args): raise TypeError(f"{cls.__name__} got multiple values for argument {key!r}") 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', }
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