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# Licensed under the LGPL: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html
# For details: https://github.com/PyCQA/astroid/blob/main/LICENSE
# Copyright (c) https://github.com/PyCQA/astroid/blob/main/CONTRIBUTORS.txt
from __future__ import annotations
import collections
from typing import TYPE_CHECKING
from astroid.context import _invalidate_cache
if TYPE_CHECKING:
from astroid import NodeNG
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.
Based on its usage in AstroidManager.brain, it should not be reinstantiated.
"""
def __init__(self):
self.transforms = collections.defaultdict(list)
def _transform(self, node: NodeNG) -> NodeNG:
"""Call matching transforms for the given node if any and return the
transformed node.
"""
cls = node.__class__
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:
_invalidate_cache()
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) -> 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) -> 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.
"""
return self._visit(module)