Using a Scheduler Before Calling `set_timestep`?

[ericspod]

Here the num_inference_steps attribute is None so if a DDIMScheduler instance is created an exception will be raised if step is called before set_timesteps is used to set the attribute. Should this be initalised in the constructor to be the same as timesteps?

If an instance of PNDMScheduler is created and step is called without set_timesteps being called, this will not raise an error but will default to 0 timesteps and do nothing.

The step method of a DDPMScheduler instance can be called without first calling set_timestep so all three behave differently. I would suggest whenever possible that an object should be usable immediately after creation and not require an initialising method to be called separately, so should we regularise on the DDPMScheduler behaviour?

[marksgraham]

Agree we should standardise, it seems sensible to initalise to the number of training timesteps as in the DDPM scheduler