Improve typing in engine

[vfdev-5]

🚀 Feature

The following code may be fail if max_epochs is None:

ignite/ignite/engine/engine.py

Lines 839 to 842 in a756f9c

	"Current iteration: {} vs Total iterations to run : {}".format(
	self.state.iteration,
	self.state.epoch_length * self.state.max_epochs, # type: ignore[operator]
	)

ignite/ignite/engine/engine.py

Lines 562 to 566 in a756f9c

	is_done_count = (
	state.epoch_length is not None
	and state.iteration >= state.epoch_length * state.max_epochs # type: ignore[operator]
	)
	is_done_epochs = state.max_epochs is not None and state.epoch >= state.max_epochs

Maybe, we have to add additional check of max_epochs is not None and remove # type: ignore[operator].

@gruebel what do you think ?

[gruebel]

I took a very long view on the code and I think it is a really good idea to check for max_epochs is not None, because right now, there can be edge cases like max_epochs is None and epoch_length is not None this will result in a Runtime Error in the _is_done method.

ignite/ignite/engine/engine.py

Lines 560 to 567 in 3affd95

	def _is_done(state: State) -> bool:
	is_done_iters = state.max_iters is not None and state.iteration >= state.max_iters
	is_done_count = (
	state.epoch_length is not None
	and state.iteration >= state.epoch_length * state.max_epochs # type: ignore[operator]
	)
	is_done_epochs = state.max_epochs is not None and state.epoch >= state.max_epochs
	return is_done_iters or is_done_count or is_done_epochs

and as long as the _is_done check doesn't raise an error here max_epochs will also be not None

ignite/ignite/engine/engine.py

Lines 835 to 843 in a756f9c

	if not self._is_done(self.state):
	warnings.warn(
	"Data iterator can not provide data anymore but required total number of "
	"iterations to run is not reached. "
	"Current iteration: {} vs Total iterations to run : {}".format(
	self.state.iteration,
	self.state.epoch_length * self.state.max_epochs, # type: ignore[operator]
	)
	)

[vfdev-5]

@gruebel thanks for the feedback. Can I assign this issue to you ?

[gruebel]

Sure 😄 will make a PR ready today or latest tomorrow.