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"""http://peter-hoffmann.com/2010/extrinsic-visitor-pattern-python-inheritance.html"""
class Node(object):
pass
class A(Node):
pass
class B(Node):
pass
class C(A, B):
pass
class Visitor(object):
def visit(self, node, *args, **kwargs):
meth = None
for cls in node.__class__.__mro__:
meth_name = 'visit_' + cls.__name__
meth = getattr(self, meth_name, None)
if meth:
break
if not meth:
meth = self.generic_visit
return meth(node, *args, **kwargs)
def generic_visit(self, node, *args, **kwargs):
print('generic_visit ' + node.__class__.__name__)
def visit_B(self, node, *args, **kwargs):
print('visit_B ' + node.__class__.__name__)
a = A()
b = B()
c = C()
visitor = Visitor()
visitor.visit(a)
visitor.visit(b)
visitor.visit(c)
### OUTPUT ###
# generic_visit A
# visit_B B
# visit_B C