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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 _newIdentifier(self):
 """ Make a new identifier for an as-yet uncreated model object. @rtype: C{int} """

        id = self._allocateID()
        self._idsToObjects[id] = self._NO_OBJECT_MARKER
        self._lastValues[id] = None
        return id