<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def _prof(self, key):
        '''Get _Prof object.
        '''
        p = self._profs.get(key, None)
        if not p:
            self._profs[key] = p = _Prof()
        return p