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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 GetKey(self, public_key_hash):
 """ Get the KeyPair belonging to the public key hash. Args: public_key_hash (UInt160):
 a public key hash to get the KeyPair for. Returns: KeyPair: If successful, the KeyPair belonging to the public key hash, otherwise None """

        if public_key_hash.ToBytes() in self._keys.keys():
            return self._keys[public_key_hash.ToBytes()]
        return None