python-patterns/visitor.py at master · andysat/python-patterns

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"""http://peter-hoffmann.com/2010/extrinsic-visitor-pattern-python-inheritance.html"""
class Node(object):
class A(Node):
class B(Node):
class C(A, B):
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__)
visitor = Visitor()
visitor.visit(a)
visitor.visit(b)
visitor.visit(c)

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