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README.md |
Simple Python Version Management: pyenv
pyenv lets you easily switch between multiple versions of Python. It's simple, unobtrusive, and follows the UNIX tradition of single-purpose tools that do one thing well.
This project was forked from rbenv and ruby-build, and modified for Python.
pyenv does...
- Let you change the global Python version on a per-user basis.
- Provide support for per-project Python versions.
- Allow you to override the Python version with an environment variable.
- Search commands from multiple versions of Python at a time. This may be helpful to test across Python versions with tox.
In contrast with pythonbrew and pythonz, pyenv does not...
- Depend on Python itself. pyenv was made from pure shell scripts. There is no bootstrap problem of Python.
- Need to be loaded into your shell. Instead, pyenv's shim
approach works by adding a directory to your
$PATH
. - Manage virtualenv. Of course, you can create virtualenv yourself, or pyenv-virtualenv to automate the process.
Table of Contents
How It Works
At a high level, pyenv intercepts Python commands using shim
executables injected into your PATH
, determines which Python version
has been specified by your application, and passes your commands along
to the correct Python installation.
Understanding PATH
When you run a command like python
or pip
, your operating system
searches through a list of directories to find an executable file with
that name. This list of directories lives in an environment variable
called PATH
, with each directory in the list separated by a colon:
/usr/local/bin:/usr/bin:/bin
Directories in PATH
are searched from left to right, so a matching
executable in a directory at the beginning of the list takes
precedence over another one at the end. In this example, the
/usr/local/bin
directory will be searched first, then /usr/bin
,
then /bin
.
Understanding Shims
pyenv works by inserting a directory of shims at the front of your
PATH
:
~/.pyenv/shims:/usr/local/bin:/usr/bin:/bin
Through a process called rehashing, pyenv maintains shims in that
directory to match every Python command across every installed version
of Python—python
, pip
, and so on.
Shims are lightweight executables that simply pass your command along
to pyenv. So with pyenv installed, when you run, say, pip
, your
operating system will do the following:
- Search your
PATH
for an executable file namedpip
- Find the pyenv shim named
pip
at the beginning of yourPATH
- Run the shim named
pip
, which in turn passes the command along to pyenv
Choosing the Python Version
When you execute a shim, pyenv determines which Python version to use by reading it from the following sources, in this order:
-
The
PYENV_VERSION
environment variable (if specified). You can use thepyenv shell
command to set this environment variable in your current shell session. -
The application-specific
.python-version
file in the current directory (if present). You can modify the current directory's.python-version
file with thepyenv local
command. -
The first
.python-version
file found (if any) by searching each parent directory, until reaching the root of your filesystem. -
The global
~/.pyenv/version
file. You can modify this file using thepyenv global
command. If the global version file is not present, pyenv assumes you want to use the "system" Python. (In other words, whatever version would run if pyenv weren't in yourPATH
.)
NOTE: You can activate multiple versions at the same time, e.g. pyenv global 3.4.1 2.7.8
. This allows for parallel usage of python2 and python3,
and is required with tools like tox
.
Locating the Python Installation
Once pyenv has determined which version of Python your application has specified, it passes the command along to the corresponding Python installation.
Each Python version is installed into its own directory under
~/.pyenv/versions
.
For example, you might have these versions installed:
~/.pyenv/versions/2.7.6/
~/.pyenv/versions/3.3.3/
~/.pyenv/versions/pypy-2.2.1/
As far as pyenv is concerned, version names are simply the directories in
~/.pyenv/versions
.
Installation
If you're on Mac OS X, consider installing with Homebrew.
The automatic installer
Visit my other project: https://github.com/yyuu/pyenv-installer
Basic GitHub Checkout
This will get you going with the latest version of pyenv and make it easy to fork and contribute any changes back upstream.
-
Check out pyenv where you want it installed. A good place to choose is
$HOME/.pyenv
(but you can install it somewhere else).$ cd $ git clone git://github.com/yyuu/pyenv.git .pyenv
-
Define environment variable
PYENV_ROOT
to point to the path where pyenv repo is cloned and add$PYENV_ROOT/bin
to your$PATH
for access to thepyenv
command-line utility.$ echo 'export PYENV_ROOT="$HOME/.pyenv"' >> ~/.bash_profile $ echo 'export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.bash_profile
Zsh note: Modify your
~/.zshenv
file instead of~/.bash_profile
. Ubuntu note: Modify your~/.bashrc
file instead of~/.bash_profile
. -
Add
pyenv init
to your shell to enable shims and autocompletion.$ echo 'eval "$(pyenv init -)"' >> ~/.bash_profile
Zsh note: Modify your
~/.zshenv
file instead of~/.bash_profile
. Ubuntu note: Modify your~/.bashrc
file instead of~/.bash_profile
. -
Restart your shell so the path changes take effect. You can now begin using pyenv.
$ exec $SHELL
-
Install Python versions into
$PYENV_ROOT/versions
. For example, to install Python 2.7.6, download and unpack the source, then run:$ pyenv install 2.7.6
NOTE: If you need to pass configure option to build, please use
CONFIGURE_OPTS
environment variable.NOTE: If you are having trouble installing a python version, please visit the wiki page about Common Build Problems
-
Rebuild the shim binaries. You should do this any time you install a new Python binary. (Examples: installing a new Python version, or installing a package that provides a binary.)
$ pyenv rehash
Upgrading
If you've installed pyenv using the instructions above, you can upgrade your installation at any time using git.
To upgrade to the latest development version of pyenv, use git pull
:
$ cd ~/.pyenv
$ git pull
To upgrade to a specific release of pyenv, check out the corresponding tag:
$ cd ~/.pyenv
$ git fetch
$ git tag
v0.1.0
$ git checkout v0.1.0
Homebrew on Mac OS X
You can also install pyenv using the Homebrew package manager for Mac OS X.
$ brew update
$ brew install pyenv
To upgrade pyenv in the future, just use upgrade
instead of install
.
After installation, you'll still need to add eval "$(pyenv init -)"
to your
profile (as stated in the caveats). You'll only ever have to do this
once.
Neckbeard Configuration
Skip this section unless you must know what every line in your shell profile is doing.
pyenv init
is the only command that crosses the line of loading
extra commands into your shell. Coming from rvm, some of you might be
opposed to this idea. Here's what pyenv init
actually does:
-
Sets up your shims path. This is the only requirement for pyenv to function properly. You can do this by hand by prepending
~/.pyenv/shims
to your$PATH
. -
Installs autocompletion. This is entirely optional but pretty useful. Sourcing
~/.pyenv/completions/pyenv.bash
will set that up. There is also a~/.pyenv/completions/pyenv.zsh
for Zsh users. -
Rehashes shims. From time to time you'll need to rebuild your shim files. Doing this on init makes sure everything is up to date. You can always run
pyenv rehash
manually. -
Installs the sh dispatcher. This bit is also optional, but allows pyenv and plugins to change variables in your current shell, making commands like
pyenv shell
possible. The sh dispatcher doesn't do anything crazy like overridecd
or hack your shell prompt, but if for some reason you needpyenv
to be a real script rather than a shell function, you can safely skip it.
To see exactly what happens under the hood for yourself, run pyenv init -
.
Uninstalling Python Versions
As time goes on, you will accumulate Python versions in your
~/.pyenv/versions
directory.
To remove old Python versions, pyenv uninstall
command to automate
the removal process.
Alternatively, simply rm -rf
the directory of the version you want
to remove. You can find the directory of a particular Python version
with the pyenv prefix
command, e.g. pyenv prefix 2.6.8
.
Command Reference
See COMMANDS.md.
Development
The pyenv source code is hosted on GitHub. It's clean, modular, and easy to understand--even if you're not a shell hacker.
Please feel free to submit Pull Requests and report bugs on the issue tracker.
Version History
See CHANGELOG.md.
License
(The MIT license)
- Copyright (c) 2013 Yamashita, Yuu
- Copyright (c) 2013 Sam Stephenson
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.