mirror of
https://github.com/python/cpython.git
synced 2025-07-16 07:45:20 +00:00
058a5adad0
Remove _preorder as alias for dispatch and call dispatch directly.
Add an extra optional argument to walk()
XXX Also comment out some code that does debugging prints.
122 lines
4.3 KiB
Python
122 lines
4.3 KiB
Python
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 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):
|
|
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 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:
|
|
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 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)
|