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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 sign(self, msg, key):
 """ Create a signature over a message :param msg: The message :param key: The key :return: A signature """

        hasher = hashes.Hash(self.hash_algorithm(), backend=default_backend())
        hasher.update(msg)
        digest = hasher.finalize()
        sig = key.sign(
            digest,
            padding.PSS(
                mgf=padding.MGF1(self.hash_algorithm()),
                salt_length=padding.PSS.MAX_LENGTH),
            utils.Prehashed(self.hash_algorithm()))
        return sig