In 1.1 we made a major BC breaking change, where the order of calling lr schedulers should be changed from

for e in range(nepochs):
  scheduler.step()
  train()

to

for e in range(nepochs):
  train()
  scheduler.step()

This silently breaks many code, and makes it impossible to write consistent code for 1.0.1 and 1.1. So I propose to add a warning in scheduler.step where it looks at the corresponding optimizer, and checks if its .step has been called.

If it has not been called, this is a sign that the user is using scheduler.step() with the old pattern. I can't think of a reasonable case where this would detect a false positive.