85 lines
3.2 KiB
Python
85 lines
3.2 KiB
Python
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# Copyright (c) 2015-2016 Claudiu Popa <pcmanticore@gmail.com>
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# Licensed under the LGPL: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html
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# For details: https://github.com/PyCQA/astroid/blob/master/COPYING.LESSER
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import collections
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import warnings
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class TransformVisitor(object):
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"""A visitor for handling transforms.
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The standard approach of using it is to call
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:meth:`~visit` with an *astroid* module and the class
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will take care of the rest, walking the tree and running the
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transforms for each encountered node.
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"""
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def __init__(self):
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self.transforms = collections.defaultdict(list)
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def _transform(self, node):
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"""Call matching transforms for the given node if any and return the
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transformed node.
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"""
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cls = node.__class__
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if cls not in self.transforms:
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# no transform registered for this class of node
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return node
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transforms = self.transforms[cls]
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orig_node = node # copy the reference
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for transform_func, predicate in transforms:
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if predicate is None or predicate(node):
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ret = transform_func(node)
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# if the transformation function returns something, it's
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# expected to be a replacement for the node
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if ret is not None:
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if node is not orig_node:
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# node has already be modified by some previous
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# transformation, warn about it
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warnings.warn('node %s substituted multiple times' % node)
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node = ret
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return node
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def _visit(self, node):
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if hasattr(node, '_astroid_fields'):
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for field in node._astroid_fields:
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value = getattr(node, field)
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visited = self._visit_generic(value)
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setattr(node, field, visited)
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return self._transform(node)
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def _visit_generic(self, node):
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if isinstance(node, list):
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return [self._visit_generic(child) for child in node]
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elif isinstance(node, tuple):
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return tuple(self._visit_generic(child) for child in node)
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return self._visit(node)
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def register_transform(self, node_class, transform, predicate=None):
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"""Register `transform(node)` function to be applied on the given
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astroid's `node_class` if `predicate` is None or returns true
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when called with the node as argument.
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The transform function may return a value which is then used to
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substitute the original node in the tree.
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"""
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self.transforms[node_class].append((transform, predicate))
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def unregister_transform(self, node_class, transform, predicate=None):
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"""Unregister the given transform."""
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self.transforms[node_class].remove((transform, predicate))
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def visit(self, module):
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"""Walk the given astroid *tree* and transform each encountered node
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Only the nodes which have transforms registered will actually
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be replaced or changed.
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"""
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module.body = [self._visit(child) for child in module.body]
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return self._transform(module)
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