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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def visitor(arg_type):
 """Decorator that creates a visitor method."""


    def decorator(fn):
        declaring_class = _declaring_class(fn)
        _methods[(declaring_class, arg_type)] = fn

        # Replace all decorated methods with _visitor_impl
        return _visitor_impl

    return decorator