code: def get_computation(self,
                          message: Message,
                          transaction_context: 'BaseTransactionContext') -> 'BaseComputation':
          
          if self.computation_class is None:
              raise AttributeError("No `computation_class` has been set for this State")
          else:
              computation = self.computation_class(self, message, transaction_context)
          return computation
docs: Return a computation instance for the given `message` and `transaction_context`