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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 subscribe(self, tag=None, match_type=None):
        '''
        Subscribe to events matching the passed tag.

        If you do not subscribe to a tag, events will be discarded by calls to
        get_event that request a different tag. In contexts where many different
        jobs are outstanding it is important to subscribe to prevent one call
        to get_event from discarding a response required by a subsequent call
        to get_event.
        '''
        if tag is None:
            return
        match_func = self._get_match_func(match_type)
        self.pending_tags.append([tag, match_func])