[python-package] “python_requires” should be set with “>=3.5”, as lightgbm 3.3.2 is not compatible with all Python versions.

[PyVCEchecker]

Description

Currently, the keyword argument python_requires of setup() is not set, and thus it is assumed that this distribution is compatible with all Python versions.
However, I found it is not compatible with Python 2. My local Python version is 2.7, and I encounter the following error when executing “pip install lightgbm”

Collecting lightgbm
  Downloading lightgbm-3.3.2.tar.gz (1.5 MB)
     |████████████████████████████████| 1.5 MB 233 kB/s 
    ERROR: Command errored out with exit status 1:
     command: /usr/local/bin/python -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-O0hSCR/lightgbm/setup.py'"'"'; __file__='"'"'/tmp/pip-install-O0hSCR/lightgbm/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-pip-egg-info-TZ3SVN
         cwd: /tmp/pip-install-O0hSCR/lightgbm/
    Complete output (6 lines):
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-install-O0hSCR/lightgbm/setup.py", line 38
        def find_lib() -> List[str]:
                       ^
    SyntaxError: invalid syntax
    ----------------------------------------
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.

I noticed that setup.py used the syntax feature Type Hints. The feature is only compatible with Python 3, resulting in installation failure of lightgbm in Python 2.7.

Way to fix:
modify setup() in setup.py, add python_requires keyword argument:

setup(…
     python_requires=">=3.5"
     …)

Thanks for your attention.
Best regrads,
PyVCEchecker

[jameslamb]

Thanks very much for using LightGBM and for the report, @PyVCEchecker !

We have historically resisted including a floor with python_requires, but I agree that in this case it would take significant effort to get the package working on Python 2.7, and from maintainers' perspective here lightgbm does not support Python 2 (as of #3581).

I'd support a pull request that adds `python_requires='>=3.5'. Would you like to submit one?

[github-actions]

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