code: def GetKey(self, public_key_hash):
          
          if public_key_hash.ToBytes() in self._keys.keys():
              return self._keys[public_key_hash.ToBytes()]
          return None
docs: 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