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# coding=utf-8
from __future__ import unicode_literals, absolute_import
from .ast import BaseNode
class Visitor(object):
'''Read-only visitor pattern.
Subclass this to gather information from an AST.
To generally define which nodes not to descend in to, overload
`generic_visit`.
To handle specific node types, add methods like `visit_Pattern`.
If you want to still descend into the children of the node, call
`generic_visit` of the superclass.
'''
def visit(self, node):
if isinstance(node, list):
for child in node:
self.visit(child)
return
if not isinstance(node, BaseNode):
return
nodename = type(node).__name__
visit = getattr(self, 'visit_{}'.format(nodename), self.generic_visit)
visit(node)
def generic_visit(self, node):
for propname, propvalue in vars(node).items():
self.visit(propvalue)
class Transformer(Visitor):
'''In-place AST Transformer pattern.
Subclass this to create an in-place modified variant
of the given AST.
If you need to keep the original AST around, pass
a `node.clone()` to the transformer.
'''
def visit(self, node):
if not isinstance(node, BaseNode):
return node
nodename = type(node).__name__
visit = getattr(self, 'visit_{}'.format(nodename), self.generic_visit)
return visit(node)
def generic_visit(self, node):
for propname, propvalue in vars(node).items():
if isinstance(propvalue, list):
new_vals = []
for child in propvalue:
new_val = self.visit(child)
if new_val is not None:
new_vals.append(new_val)
# in-place manipulation
propvalue[:] = new_vals
elif isinstance(propvalue, BaseNode):
new_val = self.visit(propvalue)
if new_val is None:
delattr(node, propname)
else:
setattr(node, propname, new_val)
return node
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