[CLI] Shorthand notation to instantiate callbacks [3/3]

[tchaton]

What does this PR do?

Part of #7250
Implements the feature request in jsonargparse: omni-us/jsonargparse#85

co-author: @carmocca

• Add support for multiple callbacks to be provided.
• Automatically merge callbacks if provided with lists and class_paths.

python script.py fit --trainer.callbacks=LearningRateMonitor --trainer.callbacks.logging_interval=epoch --trainer.callbacks.log_momentum=True --trainer.callbacks=ModelCheckpoint --trainer.callbacks.monitor=loss

Does your PR introduce any breaking changes? If yes, please list them.

None

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[codecov]

Codecov Report

Merging #8815 (afcc4ba) into master (f87b2ef) will decrease coverage by 49%.
The diff coverage is 34%.

@@           Coverage Diff            @@
##           master   #8815     +/-   ##
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- Coverage      93%     43%    -49%     
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  Files         175     175             
  Lines       14402   14543    +141     
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- Hits        13342    6319   -7023     
- Misses       1060    8224   +7164     

[carmocca]

Can you add to the post the following?:

• Motivation
• What's new
• What was changed

[pep8speaks]

Hello @tchaton! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2021-08-12 07:21:22 UTC

[tchaton]

User can registered their own callbacks. Somehow it doesn't work within the tests.

from unittest import mock
from pytorch_lightning import Callback
from pytorch_lightning.utilities.cli import CALLBACK_REGISTRIES, LightningCLI
from tests.helpers import BoringModel


class CustomCallback(Callback):
    pass

CALLBACK_REGISTRIES(cls=CustomCallback, override=True)

with mock.patch("sys.argv", ["any.py", "--trainer.callbacks=[{'class_path': test.CustomCallback}]"]):
    cli = LightningCLI(BoringModel, trainer_defaults=dict(fast_dev_run=True), run=False)
    callbacks = [c for c in cli.trainer.callbacks if isinstance(c, CustomCallback)]
    assert len(callbacks) == 1