code: def forward(self, data_batch, is_train=None):
          
          assert self.binded and self.params_initialized
          self.switch_bucket(data_batch.bucket_key, data_batch.provide_data,
                             data_batch.provide_label)
          self._curr_module.forward(data_batch, is_train=is_train)
docs: Forward computation.
  
          Parameters
          ----------
          data_batch : DataBatch
          is_train : bool
              Defaults to ``None``, in which case `is_train` is take as ``self.for_training``.