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authorJeremy Hylton <jeremy@alum.mit.edu>2000-03-06 18:49:31 (GMT)
committerJeremy Hylton <jeremy@alum.mit.edu>2000-03-06 18:49:31 (GMT)
commited9586174de17e4841e156a3a59fa283f23da1e2 (patch)
tree5cdb77d721aa2d303f8561352b38588c1f47744e /Lib
parent9cb083b957ad16183e2b74f8090f77ffe11c8feb (diff)
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factor out the tree walking/visitor code that was in compile.py
Diffstat (limited to 'Lib')
-rw-r--r--Lib/compiler/visitor.py127
1 files changed, 127 insertions, 0 deletions
diff --git a/Lib/compiler/visitor.py b/Lib/compiler/visitor.py
new file mode 100644
index 0000000..5bdf108
--- /dev/null
+++ b/Lib/compiler/visitor.py
@@ -0,0 +1,127 @@
+from tools import ast
+
+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 particular child node. If the visitor method
+ returns a true value, the ASTVisitor will not traverse the child
+ nodes.
+
+ XXX The interface for controlling the preorder walk needs to be
+ re-considered. The current interface is convenient for visitors
+ that mostly let the ASTVisitor do everything. For something like
+ a code generator, where you want to walk to occur in a specific
+ order, it's a pain to add "return 1" to the end of each method.
+ """
+
+ VERBOSE = 0
+
+ def __init__(self):
+ self.node = None
+ self._cache = {}
+
+ def preorder(self, tree, visitor):
+ """Do preorder walk of tree using visitor"""
+ self.visitor = visitor
+ visitor.visit = self._preorder
+ self._preorder(tree)
+
+ def _preorder(self, node, *args):
+ stop = apply(self.dispatch, (node,) + args)
+ if stop:
+ return
+ for child in node.getChildren():
+ if isinstance(child, ast.Node):
+ self._preorder(child)
+
+ def postorder(self, tree, visitor):
+ """Do preorder walk of tree using visitor"""
+ self.visitor = visitor
+ visitor.visit = self._postorder
+ self._postorder(tree)
+
+ def _postorder(self, tree, *args):
+ for child in node.getChildren():
+ if isinstance(child, ast.Node):
+ self._postorder(child)
+ apply(self.dispatch, (node,) + args)
+
+ 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 > 0:
+ if self.VERBOSE == 1:
+ if meth == 0:
+ print "dispatch", className
+ else:
+ print "dispatch", className, (meth and meth.__name__ or '')
+ if meth:
+ return apply(meth, (node,) + args)
+
+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 incremently, and get feedback on what
+ you still have to do.
+ """
+ examples = {}
+
+ def dispatch(self, node, *args):
+ self.node = node
+ className = node.__class__.__name__
+ meth = getattr(self.visitor, 'visit' + className, None)
+ if self.VERBOSE > 0:
+ if self.VERBOSE > 1:
+ print "dispatch", className, (meth and meth.__name__ or '')
+ if meth:
+ return apply(meth, (node,) + args)
+ elif self.VERBOSE > 0:
+ klass = node.__class__
+ if self.examples.has_key(klass):
+ return
+ self.examples[klass] = klass
+ print
+ print klass
+ for attr in dir(node):
+ if attr[0] != '_':
+ print "\t", "%-12.12s" % attr, getattr(node, attr)
+ print
+
+_walker = ASTVisitor
+def walk(tree, visitor, verbose=None):
+ w = _walker()
+ if verbose is not None:
+ w.VERBOSE = verbose
+ w.preorder(tree, visitor)
+ return w.visitor
+
+def dumpNode(node):
+ print node.__class__
+ for attr in dir(node):
+ if attr[0] != '_':
+ print "\t", "%-10.10s" % attr, getattr(node, attr)