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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 _default_client(jws_client, reactor, key, alg):
 """ Make a client if we didn't get one. """

    if jws_client is None:
        pool = HTTPConnectionPool(reactor)
        agent = Agent(reactor, pool=pool)
        jws_client = JWSClient(HTTPClient(agent=agent), key, alg)
    return jws_client