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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 assert_trigger(self, session, protocol):
 """Asserts software or hardware trigger. Corresponds to viAssertTrigger function of the VISA library. :param session: Unique logical identifier to a session. :param protocol: Trigger protocol to use during assertion. (Constants.PROT*) :return: return value of the library call. :rtype: :class:`pyvisa.constants.StatusCode` """

        try:
            return self.sessions[session].assert_trigger(protocol)

        except KeyError:
            return constants.StatusCode.error_invalid_object