Stepwise LR scheduler

[01AbhiSingh]

What does this PR do?

Fixes #<17544>

Hii @awaelchli. Can you please verify the changes I made. If they are correct then i will take up and correct any failing tests also.

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📚 Documentation preview 📚: https://pytorch-lightning--20211.org.readthedocs.build/en/20211/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81%. Comparing base (5be58f6) to head (3c48c9e).
Report is 14 commits behind head on master.

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HEAD has 553 uploads less than BASE

Flag	BASE (5be58f6)	HEAD (3c48c9e)
cpu	147	21
lightning	106	16
pytest	87	2
python3.9	43	6
python3.10	42	6
lightning_fabric	25	0
gpu	4	2
python3.11	42	6
python3.12	20	3
pytorch2.1	38	12
pytest-full	64	21
pytorch2.3	9	3
pytorch_lightning	20	7
pytorch2.2	9	3
pytorch2.4	8	3

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #20211     +/-   ##
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- Coverage      89%      81%     -8%     
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  Files         267      264      -3     
  Lines       23084    23029     -55     
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- Hits        20585    18618   -1967     
- Misses       2499     4411   +1912     

[01AbhiSingh]

Hii @Borda. Do I need to make any kind of changes in the PR ?

[lantiga]

This looks good, thank you for the contribution @01AbhiSingh

Ideally we could add a test to verify the behavior described in #17544. The current test suite can't detect the current change and this is usually a sign of insufficient coverage. Would you be willing to contribute such test?

[01AbhiSingh]

Yes, sure let me look into it.

[01AbhiSingh]

Hi @lantiga , Do you want a new test written from scratch or need me to make the necessary changes in a preexisting file? All the tests have been passed. If the changes need to be made in a preexisting file, it would be very helpful if you could point out the test in which I need to make the changes, as all the tests have been passed, and due to that, I can't find the test.

[lantiga]

hey @01AbhiSingh sorry for the wait

You can take inspiration from:

pytorch-lightning/tests/tests_pytorch/trainer/optimization/test_optimizers.py

Line 459 in b0aa504

def test_lr_scheduler_epoch_step_frequency(mocked_sched, check_val_every_n_epoch, tmp_path):

and add a new test where scheduling goes across epoch boundaries. Maybe @falckt can help too?

[lantiga]

@01AbhiSingh the test looks good! feel free to add it to test_optimizers.py and we should be ok

[01AbhiSingh]

Done. sorry I was bogged down by few things. But, a lot of new PRs for all those issues coming your way now.

[lantiga]

there's an issue with mocked_sched that is undefined in the test, other than that things look good

[01AbhiSingh]

there's an issue with mocked_sched that is undefined in the test, other than that things look good

do you mean I need to add fixture to the test function's parameters.

@pytest.fixture
def mocked_sched(mocker):
    return mocker.patch('torch.optim.lr_scheduler.StepLR.step')

[lantiga]

That's right, you can also decorate the test with

from unittest.mock import patch

...

@patch("torch.optim.lr_scheduler.StepLR.step")
def test_lr_scheduler_step_across_epoch_boundaries(mocked_sched, tmp_path):
    ...

this should work

[01AbhiSingh]

Done please check

[lantiga]

Hey @01AbhiSingh can you import LightningModule here?

https://github.com/Lightning-AI/pytorch-lightning/pull/20211/files#diff-3c3f104dbdd06271c9e6e6d4fdf61398458148412401dd55a9bac1e9b5f913a8R19

Change:

from lightning.pytorch import Trainer

to

from lightning.pytorch import Trainer, LightningModule

this should fix the failing test

[01AbhiSingh]

Yeah, my bad. Forgot to add it even after seeing it. Done, please check.

[01AbhiSingh]

https://github.com/Lightning-AI/pytorch-lightning/actions/runs/12291356552/job/34299991507?pr=20211#:~:text=FAILED%20utilities/test_data.py%3A%3Atest_update_dataloader_typerror_custom_exception%20%2D%20AssertionError%3A%20Regex%20pattern%20did%20not%20match.

This is the test that is currently failing.

def train_dataloader(self):
           # Create a simple dataset for testing
           x = torch.randn(21, 32)  # 7 batches of size 3
           y = torch.randn(21, 2)
           return DataLoader(TensorDataset(x, y), batch_size=3)

should I add this and try to run the test again ?

[lantiga]

Go for it : )

You can also run this kind of test locally with pytest tests/tests_pytorch/<test_file>.py::<name_of_test> to make things quicker on your end. This test in particular can be ran on any machine (and you can use Lightning Studios for free if you want to run on GPUs ofc)

[01AbhiSingh]

Go for it : )

You can also run this kind of test locally with pytest tests/tests_pytorch/<test_file>.py::<name_of_test> to make things quicker on your end. This test in particular can be ran on any machine (and you can use Lightning Studios for free if you want to run on GPUs ofc)

I actually tried to run the test locally with the method you suggested but this error keeps showing up ERROR: file or directory not found: tests/tests_pytorch/test_optimizers.py anyway I am trying to solve this problem on my local env.

Edit: I've solved this problem, will now update the PR only when it's running perfectly on my local environment. Thanks :)

Another Edit 😝 : updated the PR please check

[01AbhiSingh]

Test passing on my local environment but not in the PR in the repo.