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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 hijack_attr(self, attr_name):
 """Hijack an attribute on the target object. Updates the underlying class and delegating the call to the instance. This allows specially-handled attributes like __call__, __enter__, and __exit__ to be mocked on a per-instance basis. :param str attr_name: the name of the attribute to hijack """

        if not self._original_attr(attr_name):
            setattr(
                self.obj.__class__,
                attr_name,
                _proxy_class_method_to_instance(
                    getattr(self.obj.__class__, attr_name, None), attr_name
                ),
            )