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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 verify(self):
 """Verifies expectations on all doubled objects. :raise: ``MockExpectationError`` on the first expectation that is not satisfied, if any. """


        if self._is_verified:
            return

        for proxy in self._proxies.values():
            proxy.verify()

        self._is_verified = True