Migrate to f-strings for the Python code

[StrikerRUS]

Migrate all Python code from old-fashioned format() functions, formatting % operators and simple concatenations (+) to modern f-strings (brief guide). They are known to be the fastest approach and also increase code readability.

Source: https://cito.github.io/blog/f-strings/.

They are supported starting from Python 3.6 which is the oldest Python version LightGBM officially supports:

LightGBM/python-package/setup.py

Lines 374 to 378 in 9cab93a

	'Programming Language :: Python :: 3',
	'Programming Language :: Python :: 3.6',
	'Programming Language :: Python :: 3.7',
	'Programming Language :: Python :: 3.8',
	'Programming Language :: Python :: 3.9',

If you're interested in contributing, you do not need to fix all files at once. Pull requests that address all replacements in one file are mostly welcomed!

Refer to #4137 for the example PR.

• .\.ci\get_workflow_status.py (https://github.com/microsoft/LightGBM/pull/4436/files#r663508231)
• .\.nuget\create_nuget.py ([python] Migrated to f-strings for .\.nuget\create_nuget.py #4136 #4162)
• .\docs\conf.py ([python] added f-strings to docs/conf.py #4147)
• .\examples\python-guide\advanced_example.py ([python] Improving the syntax of the fstrings in the file: .\examples\python-guide\advanced_example.py #4386)
• .\examples\python-guide\logistic_regression.py ([python-package] use f-strings for concatenation in examples/python-guide/logistic_regression.py #4356)
• .\examples\python-guide\plot_example.py ([python-package] f-string format updated in plot_example.py #4421)
• .\examples\python-guide\simple_example.py ([python] Improving the syntax of prints in simple_example.py and sklearn_example.py #4396)
• .\examples\python-guide\sklearn_example.py ([python] Improving the syntax of prints in simple_example.py and sklearn_example.py #4396)
• .\examples\python-guide\dask\binary-classification.py
• .\examples\python-guide\dask\multiclass-classification.py
• .\examples\python-guide\dask\prediction.py
• .\examples\python-guide\dask\ranking.py
• .\examples\python-guide\dask\regression.py
• .\helpers\check_dynamic_dependencies.py
• .\helpers\parameter_generator.py ([python] added f-strings to helpers/parameter_generator.py #4146)
• .\python-package\setup.py ([python] added f-strings to python-package/setup.py #4145)
• .\python-package\lightgbm\basic.py ([python] added f-string to python-package/lightgbm/basic.py #4143)
• .\python-package\lightgbm\callback.py ([python] added f-string to python-package/lightgbm/callback.py #4142)
• .\python-package\lightgbm\compat.py
• .\python-package\lightgbm\dask.py ([python] added f-strings to python-package/lightgbm/dask.py #4144)
• .\python-package\lightgbm\engine.py ([python] added f-strings to python-package/lightgbm/engine.py #4258)
• .\python-package\lightgbm\libpath.py ([ci] use f-strings in libpath.py #4137)
• .\python-package\lightgbm\plotting.py (Migrate to f-strings in python-package\lightgbm\plotting.py (#4136) #4279)
• .\python-package\lightgbm\sklearn.py ([python] Migrate to f-strings in python-package/lightgbm/sklearn.py #4188)
• .\python-package\lightgbm\__init__.py
• .\tests\cpp_test\test.py
• .\tests\c_api_test\test_.py (improved the string formatting syntax #4287)
• .\tests\python_package_test\test_basic.py ([python] improving the syntax of the fstring in the file : tests/python_package_test/test_basic.py #4312)
• .\tests\python_package_test\test_consistency.py ([python-package] updated test_consistency.py to use f-strings #4348)
• .\tests\python_package_test\test_dask.py ([python] improving the syntax of the fstring in the file : tests/python_package_test/test_dask.py #4358)
• .\tests\python_package_test\test_dual.py
• .\tests\python_package_test\test_engine.py ([python-package] convert string concatenation to f-strings in test_engine.py (fixes #4136) #4436)
• .\tests\python_package_test\test_plotting.py (Updated tests/python_package_test/test_plotting.py to use f-strings #4359)
• .\tests\python_package_test\test_sklearn.py
• .\tests\python_package_test\test_utilities.py
• .\tests\python_package_test\utils.py
• .\tests\python_package_test\__init__.py

[nishitjain1204]

I can work on this if no one is assigned

[NovusEdge]

I would like to take this one up if no one's assigned.

[StrikerRUS]

@coldkillerr @NovusEdge Thanks! Sure, please feel free to pick up any file(s) you like!

[akshitadixit]

Hi may I please work on this?

[jameslamb]

@akshitadixit yes please! We'd be grateful for the help.

Please only submit pull requests for a single file, and please check the list of open pull requests at https://github.com/microsoft/LightGBM/pulls since there are a few related to this issue already open.

[jameslamb]

Oh also, the code in python-package is higher priority than the tests or examples.

[akshitadixit]

Sure, I will keep all of this in mind.

[sayantan1410]

Hi, may i work on this issue ?

[jameslamb]

Sure, thank you! Please only submit a pull request for one file at a time. @ me if you have any questions.

[sayantan1410]

Thank you so much @jameslamb

[akshitadixit]

Hey, please add a checkmark on the following files since they have no strings that need to be migrated:

• .\python-package\lightgbm\compat.py
• .\tests\python_package_test_init_.py
• .\tests\python_package_test\utils.py

[jameslamb]

ah yes you're right, thanks very much @akshitadixit !

[sagnik1511]

Hello, can I contribute to this issue ??
I want to update .\examples\python-guide\logistic_regression.py this file.

[jameslamb]

Yes please! Thanks for the help @sagnik1511

[sagnik1511]

Thanks, @jameslamb for letting me collaborate !
Do check the PR.
Thank You :)

[sayantan1410]

Hey, May I work on this file: .\examples\python-guide\advanced_example.py ?
@jameslamb

[jameslamb]

@sayantan1410 thanks for all your help! You can work on any file mentioned in this issue.

[sayantan1410]

Thank you !!
@jameslamb

[amanjha8100]

Hey, can I contribute to this issue?
.\examples\python-guide\plot_example.py
@jameslamb

[jameslamb]

Yes please, we'd be grateful for the help.

[amanjha8100]

Thanks, @jameslamb for letting me contribute !
Do check the PR.
Thank You :)

[amanjha8100]

Hey @jameslamb is there any other file that needs changing, I am unable to find any? Do we need to use regex with f-strings in .\helpers\check_dynamic_dependencies.py

[jameslamb]

Hey @jameslamb is there any other file that needs changing, I am unable to find any

Thanks for looking! I agree that helpers/check_dynamic_dependencies.py doesn't have any strings that need to be changed.

I updated the list in this issue's description:

• libpath.py - updated in [ci] use f-strings in libpath.py #4137
• helpers/check_dynamic_dependencies.py - I don't see any string concatenation that needs to be updated
• tests/python_package_test/test_sklearn.py - I don't see any string concatenation that needs to be updated

test_engine.py does have some places that need to be updated but those cases are somewhat complicated so I am going to take that one to close this issue.

Thanks so much for your help! We hope you'll contribute again in the future.

[amanjha8100]

Great, it was fun contributing!

[github-actions]

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