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136 lines
4.4 KiB
136 lines
4.4 KiB
# Copyright 2015 Google Inc. All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Generic visitor pattern for pytrees.
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The lib2to3 parser produces a "pytree" - syntax tree consisting of Node
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and Leaf types. This module implements a visitor pattern for such trees.
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It also exports a basic "dumping" visitor that dumps a textual representation of
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a pytree into a stream.
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PyTreeVisitor: a generic visitor pattern fo pytrees.
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PyTreeDumper: a configurable "dumper" for displaying pytrees.
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DumpPyTree(): a convenience function to dump a pytree.
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"""
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import sys
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from lib2to3 import pytree
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from yapf.yapflib import pytree_utils
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class PyTreeVisitor(object):
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"""Visitor pattern for pytree trees.
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Methods named Visit_XXX will be invoked when a node with type XXX is
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encountered in the tree. The type is either a token type (for Leaf nodes) or
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grammar symbols (for Node nodes). The return value of Visit_XXX methods is
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ignored by the visitor.
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Visitors can modify node contents but must not change the tree structure
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(e.g. add/remove children and move nodes around).
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This is a very common visitor pattern in Python code; it's also used in the
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Python standard library ast module for providing AST visitors.
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Note: this makes names that aren't style conformant, so such visitor methods
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need to be marked with # pylint: disable=invalid-name We don't have a choice
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here, because lib2to3 nodes have under_separated names.
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For more complex behavior, the visit, DefaultNodeVisit and DefaultLeafVisit
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methods can be overridden. Don't forget to invoke DefaultNodeVisit for nodes
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that may have children - otherwise the children will not be visited.
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"""
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def Visit(self, node):
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"""Visit a node."""
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method = 'Visit_{0}'.format(pytree_utils.NodeName(node))
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if hasattr(self, method):
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# Found a specific visitor for this node
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getattr(self, method)(node)
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else:
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if isinstance(node, pytree.Leaf):
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self.DefaultLeafVisit(node)
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else:
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self.DefaultNodeVisit(node)
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def DefaultNodeVisit(self, node):
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"""Default visitor for Node: visits the node's children depth-first.
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This method is invoked when no specific visitor for the node is defined.
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Arguments:
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node: the node to visit
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"""
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for child in node.children:
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self.Visit(child)
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def DefaultLeafVisit(self, leaf):
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"""Default visitor for Leaf: no-op.
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This method is invoked when no specific visitor for the leaf is defined.
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Arguments:
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leaf: the leaf to visit
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"""
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pass
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def DumpPyTree(tree, target_stream=sys.stdout):
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"""Convenience function for dumping a given pytree.
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This function presents a very minimal interface. For more configurability (for
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example, controlling how specific node types are displayed), use PyTreeDumper
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directly.
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Arguments:
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tree: the tree to dump.
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target_stream: the stream to dump the tree to. A file-like object. By
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default will dump into stdout.
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"""
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dumper = PyTreeDumper(target_stream)
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dumper.Visit(tree)
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class PyTreeDumper(PyTreeVisitor):
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"""Visitor that dumps the tree to a stream.
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Implements the PyTreeVisitor interface.
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"""
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def __init__(self, target_stream=sys.stdout):
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"""Create a tree dumper.
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Arguments:
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target_stream: the stream to dump the tree to. A file-like object. By
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default will dump into stdout.
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"""
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self._target_stream = target_stream
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self._current_indent = 0
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def _DumpString(self, s):
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self._target_stream.write('{0}{1}\n'.format(' ' * self._current_indent, s))
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def DefaultNodeVisit(self, node):
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# Dump information about the current node, and then use the generic
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# DefaultNodeVisit visitor to dump each of its children.
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self._DumpString(pytree_utils.DumpNodeToString(node))
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self._current_indent += 2
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super(PyTreeDumper, self).DefaultNodeVisit(node)
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self._current_indent -= 2
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def DefaultLeafVisit(self, leaf):
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self._DumpString(pytree_utils.DumpNodeToString(leaf))
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