Engine.run make input data optional

[vfdev-5]

🚀 Feature

In certain use-cases, for example in RL or multi-data cases, it does not make much sense to call engine.run with an artificial data that only defines epoch lenght:

trainer.run(data, max_epochs=100)

For example,

ignite/examples/reinforcement_learning/reinforce.py

Line 70 in 4759e01

timesteps = list(range(10000))

ignite/examples/reinforcement_learning/reinforce.py

Line 118 in 4759e01

trainer.run(timesteps, max_epochs=args.max_episodes)

The idea is to make data argument optional. Proposed API

trainer.run(max_epochs=100, epoch_length=10_000)

In this case, training_step(engine, batch) will receive None as batch value.

cc @sdesrozis

[sdesrozis]

Yes I understand the idea and agree that it would be great to have such a feature !

[fco-dv]

This API would seem clearer in such uses-cases, yes!