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# Copyright (c) 2015-2016, 2018 Claudiu Popa <pcmanticore@gmail.com>
# Copyright (c) 2016 Ceridwen <ceridwenv@gmail.com>
# Copyright (c) 2018 Nick Drozd <nicholasdrozd@gmail.com>
# Licensed under the LGPL: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html
# For details: https://github.com/PyCQA/astroid/blob/master/COPYING.LESSER
import collections
from functools import lru_cache
class TransformVisitor:
"""A visitor for handling transforms.
The standard approach of using it is to call
:meth:`~visit` with an *astroid* module and the class
will take care of the rest, walking the tree and running the
transforms for each encountered node.
"""
TRANSFORM_MAX_CACHE_SIZE = 10000
def __init__(self):
self.transforms = collections.defaultdict(list)
@lru_cache(maxsize=TRANSFORM_MAX_CACHE_SIZE)
def _transform(self, node):
"""Call matching transforms for the given node if any and return the
transformed node.
"""
cls = node.__class__
if cls not in self.transforms:
# no transform registered for this class of node
return node
transforms = self.transforms[cls]
for transform_func, predicate in transforms:
if predicate is None or predicate(node):
ret = transform_func(node)
# if the transformation function returns something, it's
# expected to be a replacement for the node
if ret is not None:
node = ret
if ret.__class__ != cls:
# Can no longer apply the rest of the transforms.
break
return node
def _visit(self, node):
if hasattr(node, "_astroid_fields"):
for name in node._astroid_fields:
value = getattr(node, name)
visited = self._visit_generic(value)
if visited != value:
setattr(node, name, visited)
return self._transform(node)
def _visit_generic(self, node):
if isinstance(node, list):
return [self._visit_generic(child) for child in node]
if isinstance(node, tuple):
return tuple(self._visit_generic(child) for child in node)
if not node or isinstance(node, str):
return node
return self._visit(node)
def register_transform(self, node_class, transform, predicate=None):
"""Register `transform(node)` function to be applied on the given
astroid's `node_class` if `predicate` is None or returns true
when called with the node as argument.
The transform function may return a value which is then used to
substitute the original node in the tree.
"""
self.transforms[node_class].append((transform, predicate))
def unregister_transform(self, node_class, transform, predicate=None):
"""Unregister the given transform."""
self.transforms[node_class].remove((transform, predicate))
def visit(self, module):
"""Walk the given astroid *tree* and transform each encountered node
Only the nodes which have transforms registered will actually
be replaced or changed.
"""
module.body = [self._visit(child) for child in module.body]
return self._transform(module)
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