from compiler import ast

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# XXX should probably rename ASTVisitor to ASTWalker

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# XXX can it be made even more generic?

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class ASTVisitor:

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"""Performs a depth-first walk of the AST

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The ASTVisitor will walk the AST, performing either a preorder or

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postorder traversal depending on which method is called.

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methods:

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preorder(tree, visitor)

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postorder(tree, visitor)

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tree: an instance of ast.Node

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visitor: an instance with visitXXX methods

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The ASTVisitor is responsible for walking over the tree in the

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correct order. For each node, it checks the visitor argument for

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a method named 'visitNodeType' where NodeType is the name of the

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node's class, e.g. Class. If the method exists, it is called

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with the node as its sole argument.

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The visitor method for a particular node type can control how

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child nodes are visited during a preorder walk. (It can't control

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the order during a postorder walk, because it is called _after_

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the walk has occurred.) The ASTVisitor modifies the visitor

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argument by adding a visit method to the visitor; this method can

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be used to visit a child node of arbitrary type.

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"""

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VERBOSE = 0

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def __init__(self):

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self.node = None

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self._cache = {}

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def default(self, node, *args):

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for child in node.getChildNodes():

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self.dispatch(child, *args)

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def dispatch(self, node, *args):

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self.node = node

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klass = node.__class__

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meth = self._cache.get(klass, None)

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if meth is None:

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className = klass.__name__

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meth = getattr(self.visitor, 'visit' + className, self.default)

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self._cache[klass] = meth

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## if self.VERBOSE > 0:

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## className = klass.__name__

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## if self.VERBOSE == 1:

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## if meth == 0:

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## print "dispatch", className

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## else:

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## print "dispatch", className, (meth and meth.__name__ or '')

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return meth(node, *args)

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def preorder(self, tree, visitor, *args):

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"""Do preorder walk of tree using visitor"""

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self.visitor = visitor

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visitor.visit = self.dispatch

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self.dispatch(tree, *args) # XXX *args make sense?

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class ExampleASTVisitor(ASTVisitor):

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"""Prints examples of the nodes that aren't visited

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This visitor-driver is only useful for development, when it's

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helpful to develop a visitor incrementally, and get feedback on what

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you still have to do.

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"""

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examples = {}

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def dispatch(self, node, *args):

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self.node = node

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meth = self._cache.get(node.__class__, None)

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className = node.__class__.__name__

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if meth is None:

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meth = getattr(self.visitor, 'visit' + className, 0)

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self._cache[node.__class__] = meth

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if self.VERBOSE > 1:

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print "dispatch", className, (meth and meth.__name__ or '')

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if meth:

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meth(node, *args)

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elif self.VERBOSE > 0:

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klass = node.__class__

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if klass not in self.examples:

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self.examples[klass] = klass

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print

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print self.visitor

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print klass

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for attr in dir(node):

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if attr[0] != '_':

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print "\t", "%-12.12s" % attr, getattr(node, attr)

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print

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return self.default(node, *args)

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# XXX this is an API change

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_walker = ASTVisitor

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def walk(tree, visitor, walker=None, verbose=None):

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if walker is None:

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walker = _walker()

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if verbose is not None:

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walker.VERBOSE = verbose

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walker.preorder(tree, visitor)

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return walker.visitor

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def dumpNode(node):

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print node.__class__

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for attr in dir(node):

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if attr[0] != '_':

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print "\t", "%-10.10s" % attr, getattr(node, attr)

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