Platform specific dependencies
https://setuptools.pypa.io/en/latest/userguide/dependency_management.html#platform-specific-dependencies
python_version
"enum34;python_version<'3.4'"
platform_system
"pywin32 >= 1.0;platform_system=='Windows'"
PEP 508によると取りうる値の例は、Linux, Windows, Java
👉
Environment Markers (PEP 508)
https://stackoverflow.com/a/42946495
で知った