[PEP508] Adding gpu or cuda markers in PEP 508

[Froskekongen]

This is a use case related to conditional installs of versions of packages (e.g. tensorflow or pytorch) based on the presence of a cuda installation on the system.

The suggestion is to add a cuda_installed marker as part of the Environment Markers. This would enable systems like pipenv to install tensorflow on cpu systems and tensorflow_gpu on systems where cuda is installed.

See these issues for more details: pipenv-issue, peps-issue.

[di]

Distutils-sig thread: https://mail.python.org/mm3/archives/list/distutils-sig@python.org/thread/LXLF4YSC4WUZOYRX65DW7CESIX7UUBK5/