support len(datamodule)

[williamFalcon]

Let's add support for len(datamodule) so we can get the following:

len(datamodule)

# prints:  
# train_dataloder_1:   200 samples
# train_dataloader_2:  500 samples
# tval_dataloder_1:    200 samples
# val_dataloader_2:    500 samples
# test_dataloder_1:    200 samples
# test_dataloader_2:   500 samples

cc @edenafek

[carmocca]

I think this is better suited for __str__, __len__ should aways return an int

[stale]

This issue has been automatically marked as stale because it hasn't had any recent activity. This issue will be closed in 7 days if no further activity occurs. Thank you for your contributions, Pytorch Lightning Team!

[kingyiusuen]

@carmocca I'd like to work on this. Do I need to write tests for this method?

[carmocca]

@kingyiusuen Go for it! And yes, it needs to be tested.

The idea would be to iterate over all the dataloaders defined in the datamodule and sum all their individual lengths. Note that not all *_dataloader methods might be defined and that the dataloaders might not have __len__ defined. In the latter case, I would suggest you count it as 0 and print a warning.

[kingyiusuen]

@kingyiusuen Go for it! And yes, it needs to be tested.

The idea would be to iterate over all the dataloaders defined in the datamodule and sum all their individual lengths. Note that not all *_dataloader methods might be defined and that the dataloaders might not have __len__ defined. In the latter case, I would suggest you count it as 0 and print a warning.

Just wanted to make sure, are we printing the number of batches (len(dataloader)) or number of samples (len(dataloader.dataset))?