code: def get_storage(self, hex_contract_address: str, hex_key: str, is_full: bool = False) -> str:
          
          payload = self.generate_json_rpc_payload(RpcMethod.GET_STORAGE, [hex_contract_address, hex_key, 1])
          response = self.__post(self.__url, payload)
          if is_full:
              return response
          return response['result']
docs: This interface is used to get the corresponding stored value
          based on hexadecimal contract address and stored key.
  
          :param hex_contract_address: hexadecimal contract address.
          :param hex_key: a hexadecimal stored key.
          :param is_full:
          :return: the information of contract storage.