Arch Linux User Repository

@Lone_Wolf: Right, but it makes no sense to use a global depends() when each package has it's own. At best, it's redundant. Again, this package is missing makedepends() which should be:

makedepends('python-setuptools' 'python2-setuptools')

See the setup.py.

I'm not, but I may have explained it badly.

This is a split package and has specific behaviour.

All options and directives for split packages default to the global values given in the PKGBUILD. 
Nevertheless, the following ones can be overridden within each split package’s packaging function: #pkgdesc, #arch, #url, #license, #groups, #depends, #optdepends, #provides, #conflicts, #replaces, #backup, #options, #install, and #changelog. 

full text at https://wiki.archlinux.org/index.php/PKGBUILD#pkgbase

Durning the build with makepkg both python & python2 need to be present, but once build is finished they are no longer needed.

When user installs python-polib only python3 is needed, for python2-polib it's only python2 .

@Lone_Wolf: It sounds like you're talking about makedepends() which is missing.

They don't , the depends= in the body of the PKGBUILD are used by makepkg during building, the ones in package_foo() are used at install time by pacman .

Are you using the -i / --install flag of makepkg ?

If so, never use that for split packages as it installs everything (python3 AND python2 versions in this case).

$ pacman -Qi python-polib 
Name            : python-polib
Version         : 1.1.0-2
Description     : A library to manipulate gettext files
Architecture    : any
URL             : https://pypi.python.org/pypi/polib
Licenses        : MIT
Groups          : None
Provides        : None
Depends On      : python
Optional Deps   : None
Required By     : singularity-git
Optional For    : None
Conflicts With  : None
Replaces        : None
Installed Size  : 172.08 KiB
Packager        : Unknown Packager
Build Date      : di 02 jun 2020 17:31:17 CEST
Install Date    : za 06 jun 2020 01:05:10 CEST
Install Reason  : Installed as a dependency for another package
Install Script  : No
Validated By    : SHA-256 Sum
$

Please remove the first depends() array as each package provides their own. Otherwise both packages depend on python and python2.