mirror of https://github.com/python/cpython
120 lines
4.2 KiB
Python
120 lines
4.2 KiB
Python
import sys
|
|
from compiler 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 default(self, node, *args):
|
|
for child in node.getChildren():
|
|
if isinstance(child, ast.Node):
|
|
apply(self._preorder, (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._preorder
|
|
self._preorder(tree, *args) # XXX *args make sense?
|
|
|
|
_preorder = dispatch
|
|
|
|
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
|
|
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:
|
|
return apply(meth, (node,) + args)
|
|
elif self.VERBOSE > 0:
|
|
klass = node.__class__
|
|
if not self.examples.has_key(klass):
|
|
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 apply(self.default, (node,) + args)
|
|
|
|
_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)
|