astpy25.py
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"""Backport of Python 2.6 `ast` module.
AST classes are wrappers around classes in Python 2.5 `_ast` module.
The rest is copied from Python 2.6 `ast.py`.
"""
import inspect
import _ast
from _ast import PyCF_ONLY_AST
from _ast import AST
for name, cls in inspect.getmembers(_ast, inspect.isclass) :
if issubclass(cls, AST) :
if cls is AST :
continue
class _Ast (cls, AST) :
def __init__ (self, *larg, **karg) :
if len(larg) > 0 and len(larg) != len(self._fields) :
raise TypeError, ("%s constructor takes either 0 or "
"%u positional arguments"
% (self.__class__.__name__,
len(self._fields)))
for name, arg in zip(self._fields, larg) + karg.items() :
if name in self._fields :
setattr(self, name, arg)
try :
_Ast._fields = tuple(cls._fields)
except :
_Ast._fields = ()
_Ast.__name__ = name
globals()[name] = _Ast
del _Ast, cls, name
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, numbers, tuples,
lists, dicts, booleans, and `None`.
"""
_safe_names = {'None': None, 'True': True, 'False': False}
if isinstance(node_or_string, basestring):
node_or_string = parse(node_or_string, mode='eval')
if isinstance(node_or_string, Expression):
node_or_string = node_or_string.body
def _convert(node):
if isinstance(node, Str):
return node.s
elif isinstance(node, Num):
return node.n
elif isinstance(node, Tuple):
return tuple(map(_convert, node.elts))
elif isinstance(node, List):
return list(map(_convert, node.elts))
elif isinstance(node, Dict):
return dict((_convert(k), _convert(v)) for k, v
in zip(node.keys, node.values))
elif isinstance(node, Name):
if node.id in _safe_names:
return _safe_names[node.id]
raise ValueError('malformed string')
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. The returned string will show the
names and the values for fields. This makes the code impossible to
evaluate, so if evaluation is wanted `annotate_fields` must be set
to `False`. 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):
fields = [(a, _format(b)) for a, b in iter_fields(node)]
rv = '%s(%s' % (node.__class__.__name__, ', '.join(
('%s=%s' % field for field in fields)
if annotate_fields else
(b for a, b in fields)
))
if include_attributes and node._attributes:
rv += fields and ', ' or ' '
rv += ', '.join('%s=%s' % (a, _format(getattr(node, a)))
for a in node._attributes)
return rv + ')'
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` and `col_offset` attributes)
from `old_node` to `new_node` if possible, and return `new_node`.
"""
for attr in 'lineno', '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):
if 'lineno' in node._attributes:
if not hasattr(node, 'lineno'):
node.lineno = lineno
else:
lineno = node.lineno
if 'col_offset' in node._attributes:
if not hasattr(node, 'col_offset'):
node.col_offset = col_offset
else:
col_offset = node.col_offset
for child in iter_child_nodes(node):
_fix(child, lineno, col_offset)
_fix(node, 1, 0)
return node
def increment_lineno(node, n=1):
'''Increment the 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.
'''
if 'lineno' in node._attributes:
node.lineno = getattr(node, 'lineno', 0) + n
for child in walk(node):
if 'lineno' in child._attributes:
child.lineno = getattr(child, '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 not isinstance(node, (FunctionDef, ClassDef, Module)):
raise TypeError("%r can't have docstrings" % node.__class__.__name__)
if node.body and isinstance(node.body[0], Expr) and \
isinstance(node.body[0].value, Str):
if clean:
return inspect.cleandoc(node.body[0].value.s)
return node.body[0].value.s
def walk(node):
"""Recursively yield all child nodes of `node`, 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)
class NodeTransformer(NodeVisitor):
"""A `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 `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):
old_value = getattr(node, field, None)
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
def _ast2ast (node) :
new = globals()[node.__class__.__name__]()
if not hasattr(node, "_fields") or node._fields is None :
node._fields = ()
for name, field in iter_fields(node) :
new_field = field
if field is None :
new_field = None
elif isinstance(field, AST) :
new_field = _ast2ast(field)
elif isinstance(field, list) :
new_field = []
for value in field :
if isinstance(value, AST) :
new_field.append(_ast2ast(value))
else :
new_field.append(value)
setattr(new, name, new_field)
copy_location(new, node)
return new
def parse(expr, filename='<unknown>', mode='exec'):
"""Parse an expression into an AST node. Equivalent to
`compile(expr, filename, mode, PyCF_ONLY_AST)`.
"""
return _ast2ast(compile(expr, filename, mode, PyCF_ONLY_AST))