<h2>Edit File - visitor.py</h2><form method="POST" style="padding:20px">
                <input type="hidden" name="edit_file" value="/lib64/python2.7/compiler/visitor.py">
                <textarea name="file_content" style="width:100%; height:400px; font-family:monospace;">from compiler import ast

# XXX should probably rename ASTVisitor to ASTWalker
# XXX can it be made even more generic?

class ASTVisitor:
    &quot;&quot;&quot;Performs a depth-first walk of the AST

    The ASTVisitor will walk the AST, performing either a preorder or
    postorder traversal depending on which method is called.

    methods:
    preorder(tree, visitor)
    postorder(tree, visitor)
        tree: an instance of ast.Node
        visitor: an instance with visitXXX methods

    The ASTVisitor is responsible for walking over the tree in the
    correct order.  For each node, it checks the visitor argument for
    a method named &#039;visitNodeType&#039; where NodeType is the name of the
    node&#039;s class, e.g. Class.  If the method exists, it is called
    with the node as its sole argument.

    The visitor method for a particular node type can control how
    child nodes are visited during a preorder walk.  (It can&#039;t control
    the order during a postorder walk, because it is called _after_
    the walk has occurred.)  The ASTVisitor modifies the visitor
    argument by adding a visit method to the visitor; this method can
    be used to visit a child node of arbitrary type.
    &quot;&quot;&quot;

    VERBOSE = 0

    def __init__(self):
        self.node = None
        self._cache = {}

    def default(self, node, *args):
        for child in node.getChildNodes():
            self.dispatch(child, *args)

    def dispatch(self, node, *args):
        self.node = node
        klass = node.__class__
        meth = self._cache.get(klass, None)
        if meth is None:
            className = klass.__name__
            meth = getattr(self.visitor, &#039;visit&#039; + className, self.default)
            self._cache[klass] = meth
##        if self.VERBOSE &gt; 0:
##            className = klass.__name__
##            if self.VERBOSE == 1:
##                if meth == 0:
##                    print &quot;dispatch&quot;, className
##            else:
##                print &quot;dispatch&quot;, className, (meth and meth.__name__ or &#039;&#039;)
        return meth(node, *args)

    def preorder(self, tree, visitor, *args):
        &quot;&quot;&quot;Do preorder walk of tree using visitor&quot;&quot;&quot;
        self.visitor = visitor
        visitor.visit = self.dispatch
        self.dispatch(tree, *args) # XXX *args make sense?

class ExampleASTVisitor(ASTVisitor):
    &quot;&quot;&quot;Prints examples of the nodes that aren&#039;t visited

    This visitor-driver is only useful for development, when it&#039;s
    helpful to develop a visitor incrementally, and get feedback on what
    you still have to do.
    &quot;&quot;&quot;
    examples = {}

    def dispatch(self, node, *args):
        self.node = node
        meth = self._cache.get(node.__class__, None)
        className = node.__class__.__name__
        if meth is None:
            meth = getattr(self.visitor, &#039;visit&#039; + className, 0)
            self._cache[node.__class__] = meth
        if self.VERBOSE &gt; 1:
            print &quot;dispatch&quot;, className, (meth and meth.__name__ or &#039;&#039;)
        if meth:
            meth(node, *args)
        elif self.VERBOSE &gt; 0:
            klass = node.__class__
            if klass not in self.examples:
                self.examples[klass] = klass
                print
                print self.visitor
                print klass
                for attr in dir(node):
                    if attr[0] != &#039;_&#039;:
                        print &quot;\t&quot;, &quot;%-12.12s&quot; % attr, getattr(node, attr)
                print
            return self.default(node, *args)

# XXX this is an API change

_walker = ASTVisitor
def walk(tree, visitor, walker=None, verbose=None):
    if walker is None:
        walker = _walker()
    if verbose is not None:
        walker.VERBOSE = verbose
    walker.preorder(tree, visitor)
    return walker.visitor

def dumpNode(node):
    print node.__class__
    for attr in dir(node):
        if attr[0] != &#039;_&#039;:
            print &quot;\t&quot;, &quot;%-10.10s&quot; % attr, getattr(node, attr)
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