Confusion about the use of from_config and its relation to _use_default_values #7626
Description
Describe the bug
I'm not sure if this qualifies as a bug because it depends on what the intent is behind the code. At the very least, I would classify it as peculiar behaviour. Suppose I instantiate some scheduler (doesn't matter which one) and extract (a copy of) its config to modify after:
sched = EulerDiscreteScheduler()
config = dict(sched.config)
If I modify config to have different key/vals, e.g config['beta_end'] = 0.5, and then instantiate a new scheduler from that config:
sched2 = EulerDiscreteScheduler.from_config(config)
sched2 is identical to sched, and this is also reflected by looking at the string repr of the object (i.e. beta_end is still the default value). I didn't understand why any changes in config weren't being reflected in sched2 until I realised that config contains an extra list called _use_default_values, which appears to track what kwargs were not passed into the constructor. In our case it's everything since we just used sched = EulerDiscreteScheduler():
['beta_end', 'sigma_max', 'timestep_spacing', 'interpolation_type', 'steps_offset', 'timestep_type', 'trained_betas', 'beta_start', 'sigma_min', 'beta_schedule', 'use_karras_sigmas', 'num_train_timesteps', 'prediction_type']
which means that beta_end gets ignored as per the behaviour in extract_init_dict (class ConfigMixin).
Ok so that means if we do the following:
# pass in explicit kwarg, beta_end=0.4
sched = EulerDiscreteScheduler(beta_end=0.4)
config = dict(sched.config)
config['beta_end'] = 0.5
sched2 = EulerDiscreteScheduler.from_config(config)
# this will be 0.5
print(sched2.beta_end)
then things work just fine.
I don't quite understand the intent behind this. Sure, I could work around the issue by actually instantiating the scheduler like sched2 = EulerDiscreteScheduler(**config) and that works, but I am still confused about the above because the docs describe from_config as "Instantiate a Python class from a config dictionary.", almost as if using <classname>.from_config is synonymous with instantiating a class via its constructor with <classname>(**kwargs). However, the way it works now is that config acts like a quasi-immutable dictionary (from the pov of the new scheduler object, assuming _use_default_values is inside).
Can we discuss what the intent is here? Thanks.
Reproduction
See above.
Logs
See above.System Info
Latest version as of now.
Who can help?
No response