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diff --git a/lib/python2.7/lib2to3/fixer_base.py b/lib/python2.7/lib2to3/fixer_base.py
new file mode 100644
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+++ b/lib/python2.7/lib2to3/fixer_base.py
@@ -0,0 +1,189 @@
+# Copyright 2006 Google, Inc. All Rights Reserved.
+# Licensed to PSF under a Contributor Agreement.
+
+"""Base class for fixers (optional, but recommended)."""
+
+# Python imports
+import logging
+import itertools
+
+# Local imports
+from .patcomp import PatternCompiler
+from . import pygram
+from .fixer_util import does_tree_import
+
+class BaseFix(object):
+
+    """Optional base class for fixers.
+
+    The subclass name must be FixFooBar where FooBar is the result of
+    removing underscores and capitalizing the words of the fix name.
+    For example, the class name for a fixer named 'has_key' should be
+    FixHasKey.
+    """
+
+    PATTERN = None  # Most subclasses should override with a string literal
+    pattern = None  # Compiled pattern, set by compile_pattern()
+    pattern_tree = None # Tree representation of the pattern
+    options = None  # Options object passed to initializer
+    filename = None # The filename (set by set_filename)
+    logger = None   # A logger (set by set_filename)
+    numbers = itertools.count(1) # For new_name()
+    used_names = set() # A set of all used NAMEs
+    order = "post" # Does the fixer prefer pre- or post-order traversal
+    explicit = False # Is this ignored by refactor.py -f all?
+    run_order = 5   # Fixers will be sorted by run order before execution
+                    # Lower numbers will be run first.
+    _accept_type = None # [Advanced and not public] This tells RefactoringTool
+                        # which node type to accept when there's not a pattern.
+
+    keep_line_order = False # For the bottom matcher: match with the
+                            # original line order
+    BM_compatible = False # Compatibility with the bottom matching
+                          # module; every fixer should set this
+                          # manually
+
+    # Shortcut for access to Python grammar symbols
+    syms = pygram.python_symbols
+
+    def __init__(self, options, log):
+        """Initializer.  Subclass may override.
+
+        Args:
+            options: a dict containing the options passed to RefactoringTool
+            that could be used to customize the fixer through the command line.
+            log: a list to append warnings and other messages to.
+        """
+        self.options = options
+        self.log = log
+        self.compile_pattern()
+
+    def compile_pattern(self):
+        """Compiles self.PATTERN into self.pattern.
+
+        Subclass may override if it doesn't want to use
+        self.{pattern,PATTERN} in .match().
+        """
+        if self.PATTERN is not None:
+            PC = PatternCompiler()
+            self.pattern, self.pattern_tree = PC.compile_pattern(self.PATTERN,
+                                                                 with_tree=True)
+
+    def set_filename(self, filename):
+        """Set the filename, and a logger derived from it.
+
+        The main refactoring tool should call this.
+        """
+        self.filename = filename
+        self.logger = logging.getLogger(filename)
+
+    def match(self, node):
+        """Returns match for a given parse tree node.
+
+        Should return a true or false object (not necessarily a bool).
+        It may return a non-empty dict of matching sub-nodes as
+        returned by a matching pattern.
+
+        Subclass may override.
+        """
+        results = {"node": node}
+        return self.pattern.match(node, results) and results
+
+    def transform(self, node, results):
+        """Returns the transformation for a given parse tree node.
+
+        Args:
+          node: the root of the parse tree that matched the fixer.
+          results: a dict mapping symbolic names to part of the match.
+
+        Returns:
+          None, or a node that is a modified copy of the
+          argument node.  The node argument may also be modified in-place to
+          effect the same change.
+
+        Subclass *must* override.
+        """
+        raise NotImplementedError()
+
+    def new_name(self, template=u"xxx_todo_changeme"):
+        """Return a string suitable for use as an identifier
+
+        The new name is guaranteed not to conflict with other identifiers.
+        """
+        name = template
+        while name in self.used_names:
+            name = template + unicode(self.numbers.next())
+        self.used_names.add(name)
+        return name
+
+    def log_message(self, message):
+        if self.first_log:
+            self.first_log = False
+            self.log.append("### In file %s ###" % self.filename)
+        self.log.append(message)
+
+    def cannot_convert(self, node, reason=None):
+        """Warn the user that a given chunk of code is not valid Python 3,
+        but that it cannot be converted automatically.
+
+        First argument is the top-level node for the code in question.
+        Optional second argument is why it can't be converted.
+        """
+        lineno = node.get_lineno()
+        for_output = node.clone()
+        for_output.prefix = u""
+        msg = "Line %d: could not convert: %s"
+        self.log_message(msg % (lineno, for_output))
+        if reason:
+            self.log_message(reason)
+
+    def warning(self, node, reason):
+        """Used for warning the user about possible uncertainty in the
+        translation.
+
+        First argument is the top-level node for the code in question.
+        Optional second argument is why it can't be converted.
+        """
+        lineno = node.get_lineno()
+        self.log_message("Line %d: %s" % (lineno, reason))
+
+    def start_tree(self, tree, filename):
+        """Some fixers need to maintain tree-wide state.
+        This method is called once, at the start of tree fix-up.
+
+        tree - the root node of the tree to be processed.
+        filename - the name of the file the tree came from.
+        """
+        self.used_names = tree.used_names
+        self.set_filename(filename)
+        self.numbers = itertools.count(1)
+        self.first_log = True
+
+    def finish_tree(self, tree, filename):
+        """Some fixers need to maintain tree-wide state.
+        This method is called once, at the conclusion of tree fix-up.
+
+        tree - the root node of the tree to be processed.
+        filename - the name of the file the tree came from.
+        """
+        pass
+
+
+class ConditionalFix(BaseFix):
+    """ Base class for fixers which not execute if an import is found. """
+
+    # This is the name of the import which, if found, will cause the test to be skipped
+    skip_on = None
+
+    def start_tree(self, *args):
+        super(ConditionalFix, self).start_tree(*args)
+        self._should_skip = None
+
+    def should_skip(self, node):
+        if self._should_skip is not None:
+            return self._should_skip
+        pkg = self.skip_on.split(".")
+        name = pkg[-1]
+        pkg = ".".join(pkg[:-1])
+        self._should_skip = does_tree_import(pkg, name, node)
+        return self._should_skip