Allow both `every` and `once` args to be defined in Events.*

🚀 Feature

Allow users to define both every and once arguments in Events.* The use case is I want to log the training loss at the first iteration to check that the loss makes sense or not, and then log the training loss at every iteration.

As of today per Events docs, we can use like

e = Events.ITERATION_COMPLETED(every=100) | Events.ITERATION_COMPLETED(once=1)
@engine.on(e)
def log_loss(engine):
    ...

It would be more useful if we can use like

e = Events.ITERATION_COMPLETED(every=100, once=1)
@engine.on(e)
def log_loss(engine):
    ...

Comments are welcome!

[vfdev-5]

What about allowing both every and once in Events.* ? Can you reopen for that? I think i can’t

As I said previously, I think it can be a bit misleading. On the other hand if user would like to have both, this can be done with a custom filter:

e = Events.ITERATION_COMPLETED(event_filter=lambda _, ev: (ev % 100 == 0) or (ev == 1))
@engine.on(e)
def log_loss(engine):
    ...

See https://pytorch.org/ignite/engine.html#ignite.engine.events.Events

[vfdev-5]

@ydcjeff thanks for feature request ! I was thinking about having every and once available together and IMO it can be a bit misleading inside a single event as you suggest: Events.ITERATION_COMPLETED(every=100, once=1)… However, I understand that it could be interesting to introduce something to simplify:

e = Events.ITERATION_COMPLETED(every=100) | Events.ITERATION_COMPLETED(once=1)

@sdesrozis what do you think ?