Update common.py

[willfrey]

I think _setup_common_training_handlers(...) is missing its return trainer statement at the end of it. I've added it here.

If this is in error, please just reject and close this.

Fixes #

Description:

Check list:

• New tests are added (if a new feature is added)
• New doc strings: description and/or example code are in RST format
• Documentation is updated (if required)

[vfdev-5]

@willfrey thanks for pointing out, actually all common.setup_common* are working inplace on input trainer : https://github.com/pytorch/ignite/blob/master/examples/references/classification/imagenet/code/scripts/common_training.py#L81

So, I think we need to remove all return trainer. Could you please do this ?

[willfrey]

I think that should do the trick. I removed the return trainer statements as well as the two return _helper(...) statements in the public setup_common_training_handlers function.

[vfdev-5]

Thanks @willfrey ! I fixed flake8

[willfrey]

Thanks! I made the edits directly on here, so the formatting was probably sloppy.