'Forward computation.
Parameters
data_batch : DataBatch
is_train : bool
Defaults to ``None``, in which case `is_train` is take as ``self.for_training``.'

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)
