author | jjkang |
Fri, 11 Jun 2010 15:22:40 +0800 | |
changeset 2 | 9da1e5517a66 |
parent 0 | ae805ac0140d |
permissions | -rw-r--r-- |
0
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Deepak Modgil <Deepak.Modgil@Nokia.com>
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1 |
from compiler import ast |
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2 |
|
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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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|
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class ASTVisitor: |
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"""Performs a depth-first walk of the AST |
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8 |
|
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9 |
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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|
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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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|
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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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|
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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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|
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class ExampleASTVisitor(ASTVisitor): |
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"""Prints examples of the nodes that aren't visited |
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|
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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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|
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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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84 |
meth(node, *args) |
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85 |
elif self.VERBOSE > 0: |
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86 |
klass = node.__class__ |
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87 |
if not self.examples.has_key(klass): |
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88 |
self.examples[klass] = klass |
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89 |
|
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90 |
print self.visitor |
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91 |
print klass |
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92 |
for attr in dir(node): |
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93 |
if attr[0] != '_': |
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print "\t", "%-12.12s" % attr, getattr(node, attr) |
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95 |
|
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return self.default(node, *args) |
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97 |
|
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98 |
# XXX this is an API change |
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99 |
|
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100 |
_walker = ASTVisitor |
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101 |
def walk(tree, visitor, walker=None, verbose=None): |
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102 |
if walker is None: |
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103 |
walker = _walker() |
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if verbose is not None: |
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105 |
walker.VERBOSE = verbose |
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106 |
walker.preorder(tree, visitor) |
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107 |
return walker.visitor |
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108 |
|
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109 |
def dumpNode(node): |
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110 |
print node.__class__ |
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111 |
for attr in dir(node): |
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112 |
if attr[0] != '_': |
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113 |
print "\t", "%-10.10s" % attr, getattr(node, attr) |