Change validate_every_epoch (bool) -> validate_every_epoch (int)

[vfdev-5]

New feature as discussed in #16

[alykhantejani]

Thanks, let's also get @fmassa's opinion on this before merging

[fmassa]

While I'm ok with this change, I'm thinking about one of the sentences in The Zen of Python, which reads

There should be one-- and preferably only one --obvious way to do it.

In this spirit, we would even remove the validate_every_epoch argument, and recommend using the VALIDATION_STARTING handler to perform the such checks based on epoch number (which would allow the user to perform arbitrarily complex checks given the epoch number).

What do you think?

[vfdev-5]

@fmassa I agree to remove validate_every_epoch. However VALIDATION_STARTING handler is less obvious way to do this.

[alykhantejani]

@vfdev-5 @fmassa I don't think VALIDATION_STARTING is the right handler to use if we remove validate_every_epoch. Instead you would want to use TRAINING_ITERATION_COMPLETED or TRAINING_EPOCH_COMPLETED as the VALIDATION_STARTING event is only triggered when trainer.validate() is called

[alykhantejani]

After discussions in #35 and #27 I think there is some consensus on removing this parameter altogether and providing a convenient handler that calls validate and wraps the logic for doing this every x epochs/iterations (see #42).

Closing this issue for now, let's redirect the conversation to #42