Remove 401 by use __all__

[chunyang-wen]

Proposed refactor

We can add __all__ in __init__.py file in order to remove F401 error and avoids the module imports.

{
    ...,
    'accelerator': <module 'pytorch_lightning.accelerators.accelerator' from '/pytorch-lightning/pytorch_lightning/accelerators/accelerator.py'>,
    'Accelerator': <class 'pytorch_lightning.accelerators.accelerator.Accelerator'>,
    'cpu': <module 'pytorch_lightning.accelerators.cpu' from '/pytorch-lightning/pytorch_lightning/accelerators/cpu.py'>,
    'CPUAccelerator': <class 'pytorch_lightning.accelerators.cpu.CPUAccelerator'>,
    'gpu': <module 'pytorch_lightning.accelerators.gpu' from '/pytorch-lightning/pytorch_lightning/accelerators/gpu.py'>,
    'GPUAccelerator': <class 'pytorch_lightning.accelerators.gpu.GPUAccelerator'>,
    'ipu': <module 'pytorch_lightning.accelerators.ipu' from '/pytorch-lightning/pytorch_lightning/accelerators/ipu.py'>,
    'IPUAccelerator': <class 'pytorch_lightning.accelerators.ipu.IPUAccelerator'>,
    'tpu': <module 'pytorch_lightning.accelerators.tpu' from '/pytorch-lightning/pytorch_lightning/accelerators/tpu.py'>,
    'TPUAccelerator': <class 'pytorch_lightning.accelerators.tpu.TPUAccelerator'>,
}

{
    ...,
    'Accelerator': <class 'pytorch_lightning.accelerators.accelerator.Accelerator'>,
    'CPUAccelerator': <class 'pytorch_lightning.accelerators.cpu.CPUAccelerator'>,
    'GPUAccelerator': <class 'pytorch_lightning.accelerators.gpu.GPUAccelerator'>,
    'IPUAccelerator': <class 'pytorch_lightning.accelerators.ipu.IPUAccelerator'>,
    'TPUAccelerator': <class 'pytorch_lightning.accelerators.tpu.TPUAccelerator'>,
}

Motivation

Remove annoying 401 error.

Pitch

No error reported by mypy or pre-commit

cc @Borda @justusschock @awaelchli @akihironitta @rohitgr7

[Borda]

I am not sure if want to amplify the visibility of these internal tools...

[justusschock]

What's internal there? They are supposed to be stable with 1.6 as user-interface for power users...

[chunyang-wen]

__all__ does not mean you have to expose everything (You can choose what to expose by yourself). Even you do not want to expose the modules, users can still import them. What I suggest here is to use __all__ to remove the #noqa F401 error or comment.

[akihironitta]

@chunyang-wen Sounds good to me!

---

(just for the note) I believe this is technically a breaking change for users importing all names:

from pytorch_lightning.accelerators import *
...

[ananthsub]

Some things like get_nvidia_gpu_stats are in the gpu accelerator module but not in the GPUAccelerator class definition. Will this break those imports?

[chunyang-wen]

Yes, it will break users' code if they use modules automatically imported by python.

from pytorch_lightning.accelerators import *

accelerator.blabla
cpu.blabla

for compability, we can also export the modules at the same time.

from pytorch_lightning.accelerators import accelerator
from pytorch_lightning.accelerators.accelerator import Accelerator

__all__ = ["accelerator", "Accelerator"]

[adshukla1902]

Hi, Can I start working on this issue, this will be my first contribution.

[justusschock]

I am not sure if there actually was an agreement to do this

thoughts @Lightning-AI/core-lightning