Unused attribute names in fit function

What are the following lines in model.py really doing?

if hasattr(cur_data, 'trn_sampler'): cur_data.trn_sampler.set_epoch(epoch)
if hasattr(cur_data, 'val_sampler'): cur_data.val_sampler.set_epoch(epoch)

ModelData object does not have any attributes named trn_sampler or val_sampler and neither do these attributes seem to be created at any stage. Or am I wrong about that?