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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)