1 files changed, 113 insertions, 0 deletions
diff --git a/lib/python2.7/compiler/visitor.py b/lib/python2.7/compiler/visitor.py
new file mode 100644
index 0000000..f10f560
--- /dev/null
+++ b/lib/python2.7/compiler/visitor.py
@@ -0,0 +1,113 @@
+from compiler import ast
+
+# XXX should probably rename ASTVisitor to ASTWalker
+# XXX can it be made even more generic?
+
+class ASTVisitor:
+    """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 'visitNodeType' where NodeType is the name of the
+    node'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'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.
+    """
+
+    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, 'visit' + className, self.default)
+            self._cache[klass] = meth
+##        if self.VERBOSE > 0:
+##            className = klass.__name__
+##            if self.VERBOSE == 1:
+##                if meth == 0:
+##                    print "dispatch", className
+##            else:
+##                print "dispatch", className, (meth and meth.__name__ or '')
+        return meth(node, *args)
+
+    def preorder(self, tree, visitor, *args):
+        """Do preorder walk of tree using visitor"""
+        self.visitor = visitor
+        visitor.visit = self.dispatch
+        self.dispatch(tree, *args) # XXX *args make sense?
+
+class ExampleASTVisitor(ASTVisitor):
+    """Prints examples of the nodes that aren't visited
+
+    This visitor-driver is only useful for development, when it's
+    helpful to develop a visitor incrementally, and get feedback on what
+    you still have to do.
+    """
+    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, 'visit' + className, 0)
+            self._cache[node.__class__] = meth
+        if self.VERBOSE > 1:
+            print "dispatch", className, (meth and meth.__name__ or '')
+        if meth:
+            meth(node, *args)
+        elif self.VERBOSE > 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] != '_':
+                        print "\t", "%-12.12s" % 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] != '_':
+            print "\t", "%-10.10s" % attr, getattr(node, attr)