114 lines
3.9 KiB
Python
114 lines
3.9 KiB
Python
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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 not self.examples.has_key(klass):
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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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