Python

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Python is a cross-platform interpreted programming language. Python powers Portage, eselect, equery, and many other tools in Gentoo.

Installation

Since Python is so integral to Gentoo there is little chance it is not installed. Doing so would be like removing the heart from Gentoo. There is occasion where Python must be recompiled in order to add new features or to upgrade.

USE flags

USE flags for dev-lang/python An interpreted, interactive, object-oriented programming language

bluetooth Build Bluetooth protocol support in socket module
build !!internal use only!! DO NOT SET THIS FLAG YOURSELF!, used for creating build images and the first half of bootstrapping [make stage1]
examples Install examples, usually source code
gdbm Add support for sys-libs/gdbm (GNU database libraries)
hardened Activate default security enhancements for toolchain (gcc, glibc, binutils)
ipv6 Add support for IP version 6
ncurses Add ncurses support (console display library)
readline Enable support for libreadline, a GNU line-editing library that almost everyone wants
sqlite Add support for sqliteembedded sql database
ssl Add support for SSL/TLS connections (Secure Socket Layer / Transport Layer Security)
test Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)
tk Add support for Tk GUI toolkit
verify-sig Verify upstream signatures on distfiles
wininst Install Windows executables required to create an executable installer for MS Windows.
xml Add support for XML files

Emerge

Python is slotted, which means there is more than one version Python that can be installed on a Gentoo system at the same time. Select the version to install by using an : (colon) and the package atom followed by one of the slot numbers:

For example, to install Python 3.8:

root #emerge --ask dev-lang/python:3.8

Configuration

Setting the active interpreter

The default (non-versioned) active interpreter is controlled through package dev-lang/python-exec. See python-exec wiki

Each time dev-lang/python-exec is emerged/rebuilt, use dispatch-conf, etc-update or similar to accept or deny proposed modification to /etc/python-exec/python-exec.conf (that control the default Python interpreter)

Note
Python preference to follow PYTHON_TARGETS official statement - 2021-01-30

The older way to change to the active Python (non-versioned) interpreter using the eselect python command will remain as a wrapper to python-exec.conf modification if app-eselect/eselect-python is in the @world set. See eselect-python wiki

Version upgrade

Note
Python 2.7 has reached its end-of-life by January 1, 2020, as per this official statement.

Version upgrades can be elective, or may have to happen due to a profile update.

Profile update

When a Python version becomes deprecated, or is no longer supported, it may cause a profile update to set the PYTHON_SINGLE_TARGET to a higher version. This may cause emerge conflicts when updating a system.

The easiest way to handle this is to add the new Python version to the PYTHON_TARGETS, e.g. for the transition from python3_7 to python3_8:

FILE /etc/portage/package.use
*/* PYTHON_TARGETS: python3_7 python3_8

Then update the system:

root #emerge --ask --update --newuse --deep @world

Remove the support for the previous Python version, by removing the line added to /etc/portage/package.use and rebuild the system again.

Elective version upgrade

Users may select to upgrade their Python version also by choice. Before starting ensure that the system is up to date:

root #emerge --ask --update --newuse --deep @world

To make system packages be rebuilt using the new Python implementation update the PYTHON_TARGETS and PYTHON_SINGLE_TARGET variables in /etc/portage/package.use. For example, when updating from Python 3.6 to 3.7:

FILE /etc/portage/package.use
*/* PYTHON_TARGETS: python3_7
*/* PYTHON_SINGLE_TARGET: -* python3_7

Then update the system again using the --changed-use --deep options:

root #emerge --ask --changed-use --deep @world

You may be asked to update any remaining python_targets_python3_6 USE flags as well.

Note that some popular packages still require PYTHON_SINGLE_TARGET variable to be set to python2_7 due to various dependencies.

Cleanup

 As of Jan 19, 2021, the information in this section is probably outdated. You can help the Gentoo community by verifying and updating this section.

Once the upgrade has completed, old Python implementations can be removed from the system using:

root #emerge --ask --depclean dev-lang/python

After depclean eselect python list will still show old Python versions if they were previously selected, to remove these entries run the following command:

root #eselect python cleanup
Note
The old python-updater has been removed from the Gentoo ebuild repository by this commit.

Usage

Invocation

A specific version of the Python interpreter can be invoked from the command-line directly by running:

user $python2.7

Or

user $python3.7

To execute a script with Python 2.x use the following header:

FILE /usr/local/bin/repo
#!/usr/bin/env python2
...

See also

  • Bash — the default shell on Gentoo systems and a popular shell program found on many Linux systems.
  • PipPython's package management system. It references packages available in the official Python Package Index (PyPI).

External resources