Common basics

The various eclasses in python-r1 try to follow a single design. You will probably use more than one of them, so it is worthwhile to shortly explain the common bits used by all of them, as well as the non-obvious differences between them.


The PYTHON_COMPAT variable is used by all Python eclasses, and must be declared in all ebuilds before they are inherited. It specifies the list of Python implementations supported by the package.

The valid values are:

  • pythonX_Y for CPython X.Y

  • pypy3 for PyPy3.

Typical use:

PYTHON_COMPAT=( python3_{6,7,8} pypy3 )
inherit python-single-r1


The python-any-r1, python-single-r1 and python-r1 eclasses all assume that the developer is responsible for explicitly putting the dependency strings and USE requirements in correct variables. This is meant to consistently cover packages that use Python unconditionally and conditionally, at build time and at runtime.

For python-single-r1 and python-r1, the most basic form to use Python unconditionally is to define the following:



For python-any-r1, only build-time dependencies are used:


This does not apply to distutils-r1 as it does the above assignment by default.

Python environment

The eclasses commonly use the concept of Python environment. This means a state of environment enforcing a particular Python implementation. Whenever the ebuild code is run inside this environment, EPYTHON variable indicates which implementation is being used (by its executable name, e.g. python3.8).

Additionally, PYTHON provides the absolute path to the interpreter (however, using EPYTHON is preferable whenever possible). Wrappers for python, pythonN and some common tools are provided in PATH, and /usr/bin/python etc. also enforce the specific implementation via python-exec (for programs that hardcode full path).

The environment can be either established in local scope, or globally. The local scope generally applies to multi-impl packages, and is created either by calls to python_foreach_impl from python-r1, or inside sub-phase functions in distutils-r1. The global scope setup is done via calling python_setup, either directly or via default pkg_setup in python-any-r1 and python-single-r1.