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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 get_timemachine_instance(self, key):
 """Return a TimeMachine for a related object. Take a string argument representing a ForeignKey field name, find what object was related to this one at the time of this TimeMachine and return a TimeMachine for that related object. """

        modcommit = self._get_modcommit(key)
        if not modcommit: 
            return None
        return TimeMachine(uid = modcommit.value)