Fixes https://github.com/pytorch/pytorch/issues/98921
There were two issues detected:
- `MultiStepLR`: issue is described in https://github.com/pytorch/pytorch/issues/98921, this is resolved by allowlisting `collections.Counter`
- `OneCycleLR`: `state_dict['anneal_func']` is either `<function OneCycleLR._annealing_cos at 0x7f364186f5b0>` or
`<function OneCycleLR._annealing_linear at 0x7f39aa483640>` depending on the `anneal_func` kwarg.
This leads to `WeightsUnpickler error: Unsupported class __builtin__.getattr` from the `weights_only` Unpickler.
Fixed the above in a BC-compatible manner by adding `OneCyclicLR._anneal_func_type` as a string attribute and removing `OneCyclicLR.anneal_func`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/123775
Approved by: https://github.com/albanD, https://github.com/malfet
## How to reproduce:
```py
import os
import tempfile
import torch
from torch import nn
from torch.optim import SGD
from torch.optim.lr_scheduler import CyclicLR
model = nn.Linear(100, 100)
opt = SGD(model.parameters(), lr=1.)
scheduler = CyclicLR(opt, base_lr=0.1, max_lr=0.2, scale_fn=lambda x: 0.99)
tmp = tempfile.NamedTemporaryFile(delete=False)
try:
torch.save(scheduler.state_dict(), tmp.name)
scheduler.load_state_dict(torch.load(tmp.name))
finally:
tmp.close()
os.unlink(tmp.name)
```
Error:
```
_pickle.PicklingError: Can't pickle <function <lambda> at 0x000001A51DF67600>: attribute lookup <lambda> on __main__ failed
```
## Fix:
Saving `scale_fn` to the state dict only if it is a callable object and not if it is a function or lambda.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/110931
Approved by: https://github.com/janeyx99
Fixes#42376
`torch.save` serializes bound methods inside LR scheduler resulting in large serialized file.
Test cases include checking file size, checking if the `anneal_func` is bounded and file is loaded correctly.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/102627
Approved by: https://github.com/albanD
