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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 valid(cls, token, **kwargs):
 """ Check if a token exists and has not expired :param token: the token :return: bool """

        try:
            token = yield cls.get(token)
        except couch.NotFound:
            raise Return(False)

        raise Return(token.ttl >= datetime.utcnow())