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 root)/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
PATHfor an executable file namedpip - Find the pyenv shim named
pipat 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_VERSIONenvironment variable (if specified). You can use thepyenv shellcommand to set this environment variable in your current shell session. -
The application-specific
.python-versionfile in the current directory (if present). You can modify the current directory's.python-versionfile with thepyenv localcommand. -
The first
.python-versionfile found (if any) by searching each parent directory, until reaching the root of your filesystem. -
The global
$(pyenv root)/versionfile. You can modify this file using thepyenv 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 yourPATH.)
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 pyenv 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 (should display $(pyenv root)/versions/2.5/bin/python2.5), or pyenv which 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 $(pyenv root)/versions.
For example, you might have these versions installed:
$(pyenv root)/versions/2.7.8/$(pyenv root)/versions/3.4.2/$(pyenv root)/versions/pypy-2.4.0/
As far as pyenv is concerned, version names are simply the directories in $(pyenv root)/versions.
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. Because the 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.
Installation
Prerequisites:
For pyenv to install python correctly you should install the Python build dependencies.
Homebrew on macOS
- Consider installing with Homebrew
brew update brew install pyenv
- Then follow the rest of the post-installation steps under Basic GitHub Checkout, starting with #3 ("Add
pyenv initto your shell to enable shims and autocompletion").
If you're on Windows, consider using @kirankotari's pyenv-win fork. (pyenv does not work on windows outside the Windows Subsystem for Linux)
The automatic installer
Visit my other project: https://github.com/pyenv/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
$HOME/.pyenv(but you can install it somewhere else).git clone https://github.com/pyenv/pyenv.git ~/.pyenvOptionally, try to compile dynamic bash extension to speed up pyenv. Don't worry if it fails; pyenv will still work normally:
cd ~/.pyenv && src/configure && make -C src -
Define environment variable
PYENV_ROOTto point to the path where pyenv repo is cloned and add$PYENV_ROOT/binto your$PATHfor access to thepyenvcommand-line utility.-
For bash:
echo 'export PYENV_ROOT="$HOME/.pyenv"' >> ~/.bash_profile echo 'export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.bash_profile
-
For Ubuntu Desktop:
echo 'export PYENV_ROOT="$HOME/.pyenv"' >> ~/.bashrc echo 'export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.bashrc
-
For Zsh:
echo 'export PYENV_ROOT="$HOME/.pyenv"' >> ~/.zshrc echo 'export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.zshrc
-
For Fish shell:
set -Ux PYENV_ROOT $HOME/.pyenv set -Ux fish_user_paths $PYENV_ROOT/bin $fish_user_paths
-
Proxy note: If you use a proxy, export
http_proxyandHTTPS_PROXYtoo.
-
-
Add
pyenv initto your shell to enable shims and autocompletion. Please make sureeval "$(pyenv init -)"is placed toward the end of the shell configuration file since it manipulatesPATHduring the initialization.-
For bash:
echo -e 'if command -v pyenv 1>/dev/null 2>&1; then\n eval "$(pyenv init -)"\nfi' >> ~/.bash_profile
-
For Ubuntu Desktop and Fedora:
echo -e 'if command -v pyenv 1>/dev/null 2>&1; then\n eval "$(pyenv init -)"\nfi' >> ~/.bashrc
-
For Zsh:
echo -e 'if command -v pyenv 1>/dev/null 2>&1; then\n eval "$(pyenv init -)"\nfi' >> ~/.zshrc
-
For Fish shell:
echo -e '\n\n# pyenv init\nif command -v pyenv 1>/dev/null 2>&1\n pyenv init - | source\nend' >> ~/.config/fish/config.fish
General warning: There are some systems where the
BASH_ENVvariable is configured to point to.bashrc. On such systems you should almost certainly put the above mentioned lineeval "$(pyenv init -)"into.bash_profile, and not into.bashrc. Otherwise you may observe strange behaviour, such aspyenvgetting 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 build dependencies before attempting to install a new Python version.
-
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
CONFIGURE_OPTSenvironment variable.NOTE: If you want to use proxy to download, please use
http_proxyandhttps_proxyenvironment variable.NOTE: If you are having trouble installing a python version, please visit the wiki page about Common Build Problems
Upgrading
If you've installed pyenv using homebrew, upgrade using:
brew upgrade pyenv
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 root)
git pull
To upgrade to a specific release of pyenv, check out the corresponding tag:
cd $(pyenv root)
git fetch
git tag
git checkout v0.1.0
Uninstalling pyenv
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 likepythonwill execute the system Python version, as before pyenv.
pyenv will 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
$(pyenv root)/versions/directory: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
Advanced 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
$(pyenv root)/shimsto your$PATH. -
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
pyenv rehashmanually. -
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 overridecdor hack your shell prompt, but if for some reason you needpyenvto 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 -.
If you don't want to use pyenv init and shims, you can still benefit from pyenv's ability to install Python versions for you. Just run pyenv install and you will find versions installed in $(pyenv root)/versions, which you can manually execute or symlink as required.
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.
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.
Environment variables
You can affect how pyenv operates with the following settings:
| name | default | description |
|---|---|---|
PYENV_VERSION |
Specifies the Python version to be used. Also see pyenv shell |
|
PYENV_ROOT |
~/.pyenv |
Defines the directory under which Python versions and shims reside. Also see pyenv root |
PYENV_DEBUG |
Outputs debug information. Also as: pyenv --debug <subcommand> |
|
PYENV_HOOK_PATH |
see wiki | Colon-separated list of paths searched for pyenv hooks. |
PYENV_DIR |
$PWD |
Directory to start searching for .python-version files. |
PYTHON_BUILD_ARIA2_OPTS |
Used to pass additional parameters to aria2.If the aria2c binary is available on PATH, pyenv uses aria2c instead of curl or wget to download the Python Source code. If you have an unstable internet connection, you can use this variable to instruct aria2 to accelerate the download.In most cases, you will only need to use -x 10 -k 1M as value to PYTHON_BUILD_ARIA2_OPTS environment variable |
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.
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.
Version History
See CHANGELOG.md.
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