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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 keys_by_alg_and_usage(self, issuer, alg, usage):
 """ Find all keys that can be used for a specific crypto algorithm and usage by key owner. :param issuer: Key owner :param alg: a crypto algorithm :param usage: What the key should be used for :return: A possibly empty list of keys """

        if usage in ["sig", "ver"]:
            ktype = jws_alg2keytype(alg)
        else:
            ktype = jwe_alg2keytype(alg)

        return self.get(usage, ktype, issuer)