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.
- 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
- Manage virtualenv. Of course, you can create virtualenv yourself, or pyenv-virtualenv to automate the process.
Table of Contents
- How It Works
- Command Reference
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.
When you run a command like
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
PATH, with each directory in the list separated by a colon:
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
pyenv works by inserting a directory of shims at the front of your
Through a process called rehashing, pyenv maintains shims in that
directory to match every Python command across every installed version
pip, and so on.
Shims are lightweight executables that simply pass your command along
to pyenv. So with pyenv installed, when you run, say,
operating system will do the following:
- Search your
PATHfor an executable file named
- Find the pyenv shim named
pipat the beginning of your
- 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:
PYENV_VERSIONenvironment variable (if specified). You can use the
pyenv shellcommand to set this environment variable in your current shell session.
.python-versionfile in the current directory (if present). You can modify the current directory's
.python-versionfile with the
.python-versionfile found (if any) by searching each parent directory, until reaching the root of your filesystem.
$(pyenv root)/versionfile. You can modify this file using the
pyenv globalcommand. 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 your
NOTE: You can activate multiple versions at the same time, including multiple
versions of Python2 or Python3 simultaneously. This allows for parallel usage of
Python2 and Python3, and is required with tools like
tox. For example, to set
your path to first use your
system Python and Python3 (set to 2.7.9 and 3.4.2
in this example), but also have Python 3.3.6, 3.2, and 2.5 available on your
PATH, one would first
pyenv install the missing versions, then set
global system 3.3.6 3.2 2.5. At this point, one should be able to find the full
executable path to each of these using
pyenv which, e.g.
pyenv which python2.5
$(pyenv root)/versions/2.5/bin/python2.5), or
python3.4 (should display path to system Python3). You can also specify multiple
versions in a
.python-version file, separated by newlines or any whitespace.
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
For example, you might have these versions installed:
As far as pyenv is concerned, version names are simply the directories in
Managing Virtual Environments
There is a pyenv plugin named pyenv-virtualenv which comes with various features to help pyenv users to manage virtual environments created by virtualenv or Anaconda.
activate script of those virtual environments are relying on mutating
$PATH variable of user's interactive shell, it will intercept pyenv's shim style command execution hooks.
We'd recommend to install pyenv-virtualenv as well if you have some plan to play with those virtual environments.
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).
$ git clone https://github.com/yyuu/pyenv.git ~/.pyenv
Define environment variable
PYENV_ROOTto point to the path where pyenv repo is cloned and add
$PATHfor access to the
$ echo 'export PYENV_ROOT="$HOME/.pyenv"' >> ~/.bash_profile $ echo 'export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.bash_profile
Zsh note: Modify your
~/.zshenvfile instead of
Ubuntu and Fedora note: Modify your
~/.bashrcfile instead of
pyenv initto your shell to enable shims and autocompletion. Please make sure
eval "$(pyenv init -)"is placed toward the end of the shell configuration file since it manipulates
PATHduring the initialization.
$ echo 'eval "$(pyenv init -)"' >> ~/.bash_profile
Zsh note: Modify your
~/.zshenvfile instead of
Ubuntu and Fedora note: Modify your
~/.bashrcfile instead of
General warning: There are some systems where the
BASH_ENVvariable is configured to point to
.bashrc. On such systems you should almost certainly put the abovementioned line
eval "$(pyenv init -)into
.bash_profile, and not into
.bashrc. Otherwise you may observe strange behaviour, such as
pyenvgetting into an infinite loop. See #264 for details.
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 download and install Python 2.7.8, run:
$ pyenv install 2.7.8
NOTE: If you need to pass configure option to build, please use
NOTE: If you want to use proxy to download, please use
NOTE: If you are having trouble installing a python version, please visit the wiki page about Common Build Problems
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
$ cd $(pyenv root) $ git pull
To upgrade to a specific release of pyenv, check out the corresponding tag:
$ cd $(pyenv root) $ git fetch $ git tag v0.1.0 $ git checkout v0.1.0
The simplicity of pyenv makes it easy to temporarily disable it, or uninstall from the system.
To disable pyenv managing your Python versions, simply remove the
pyenv initline from your shell startup configuration. This will remove pyenv shims directory from PATH, and future invocations like
pythonwill execute the system Python version, as before pyenv.
pyenvwill still be accessible on the command line, but your Python apps won't be affected by version switching.
To completely uninstall pyenv, perform step (1) and then remove its root directory. This will delete all Python versions that were installed under
rm -rf $(pyenv root)
If you've installed pyenv using a package manager, as a final step perform the pyenv package removal. For instance, for Homebrew:
brew uninstall pyenv
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, use
upgrade instead of
After installation, you'll need to add
eval "$(pyenv init -)" to your profile (as stated in the caveats displayed by Homebrew — to display them again, use
brew info pyenv). You only need to add that to your profile once.
Then follow the rest of the post-installation steps under "Basic GitHub Checkout" above, starting with #4 ("restart your shell so the path changes take effect").
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 root)/shimsto your
Installs autocompletion. This is entirely optional but pretty useful. Sourcing
$(pyenv root)/completions/pyenv.bashwill set that up. There is also a
$(pyenv root)/completions/pyenv.zshfor 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
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 shellpossible. The sh dispatcher doesn't do anything crazy like override
cdor hack your shell prompt, but if for some reason you need
pyenvto 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 root)/versions directory.
To remove old Python versions,
pyenv uninstall command to automate
the removal process.
rm -rf the directory of the version you want
to remove. You can find the directory of a particular Python version
pyenv prefix command, e.g.
pyenv prefix 2.6.8.
You can affect how pyenv operates with the following settings:
||Specifies the Python version to be used.
||Defines the directory under which Python versions and shims reside.
||Outputs debug information.
||see wiki||Colon-separated list of paths searched for pyenv hooks.|
||Directory to start searching for
||Used to pass aditional parameters to
In most cases, you will only need to use
The pyenv source code is hosted on GitHub. It's clean, modular, and easy to understand, even if you're not a shell hacker.
Tests are executed using Bats:
$ bats test $ bats/test/<file>.bats
Please feel free to submit pull requests and file bugs on the issue tracker.