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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...

  • Depending 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.
  • Have a configuration file. There's nothing to configure except which version of Python you want to use.
  • Manage virtualenv. Of course, you can create virtualenv yourself, or python-virtualenv to automate the process.
  • Prompt you with warnings when you switch to a project. Instead of executing arbitrary code, pyenv reads just the version name from each project. There's nothing to "trust."

Table of Contents

1 How It Works

pyenv operates on the per-user directory ~/.pyenv. Version names in pyenv correspond to subdirectories of ~/.pyenv/versions. For example, you might have ~/.pyenv/versions/2.7.3 and ~/.pyenv/versions/2.7.3.

Each version is a working tree with its own binaries, like ~/.pyenv/versions/2.7.3/bin/python2.7 and ~/.pyenv/versions/3.2.3/bin/python3.2. pyenv makes shim binaries for every such binary across all installed versions of Python.

These shims are simple wrapper scripts that live in ~/.pyenv/shims and detect which Python version you want to use. They insert the directory for the selected version at the beginning of your $PATH and then execute the corresponding binary.

Because of the simplicity of the shim approach, all you need to use pyenv is ~/.pyenv/shims in your $PATH.

2 Installation

2.1 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.

  1. Check out pyenv into ~/.pyenv.

    $ cd
    $ git clone git://github.com/yyuu/pyenv.git .pyenv
    
  2. Add ~/.pyenv/bin to your $PATH for access to the pyenv command-line utility.

    $ echo 'export PATH="$HOME/.pyenv/bin:$PATH"' >> ~/.bash_profile
    

    Zsh note: Modify your ~/.zshenv file instead of ~/.bash_profile.

  3. 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.

  4. Restart your shell so the path changes take effect. You can now begin using pyenv.

    $ exec $SHELL
    
  5. Install Python versions into ~/.pyenv/versions. For example, to install Python 2.7.3, download and unpack the source, then run:

    $ pyenv install 2.7.3
    
  6. Rebuild the shim binaries. You should do this any time you install a new Python binary (for example, when installing a new Python version, or when installing a gem that provides a binary).

    $ pyenv rehash
    

2.1.1 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

2.2 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:

  1. 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.

  2. 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.

  3. 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.

  4. 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 override cd or hack your shell prompt, but if for some reason you need pyenv to be a real script rather than a shell function, you can safely skip it.

Run pyenv init - for yourself to see exactly what happens under the hood.

3 Usage

Like git, the pyenv command delegates to subcommands based on its first argument. The most common subcommands are:

3.1 pyenv global

Sets the global version of Python to be used in all shells by writing the version name to the ~/.pyenv/version file. This version can be overridden by a per-project .pyenv-version file, or by setting the PYENV_VERSION environment variable.

$ pyenv global 2.7.3

The special version name system tells pyenv to use the system Python (detected by searching your $PATH).

When run without a version number, pyenv global reports the currently configured global version.

And also, you can specify multiple versions as global Python. Commands within these Python versions are searched by specified order.

$ pyenv global 2.7.3 3.2.3
$ pyenv global
2.7.3
3.2.3
$ pyenv which python2.7
/home/yyuu/.pyenv/versions/2.7.3/bin/python2.7
$ pyenv which python3.2
/home/yyuu/.pyenv/versions/3.2.3/bin/python3.2
$ pyenv which python
/home/yyuu/.pyenv/versions/2.7.3/bin/python

You can manage your version stack by pyenv push and pyenv pop.

$ pyenv global
2.7.3
3.2.3
$ pyenv push 3.3.0
$ pyenv global
2.7.3
3.2.3
3.3.0
$ pyenv pop
2.7.3
3.2.3

3.2 pyenv local

Sets a local per-project Python version by writing the version name to an .pyenv-version file in the current directory. This version overrides the global, and can be overridden itself by setting the PYENV_VERSION environment variable or with the pyenv shell command.

$ pyenv local rbx-1.2.4

When run without a version number, pyenv local reports the currently configured local version. You can also unset the local version:

$ pyenv local --unset

And also, you can specify multiple versions as local Python. Commands within these Python versions are searched by specified order.

$ pyenv local 2.7.3 3.2.3
$ pyenv local
2.7.3
3.2.3
$ pyenv which python2.7
/home/yyuu/.pyenv/versions/2.7.3/bin/python2.7
$ pyenv which python3.2
/home/yyuu/.pyenv/versions/3.2.3/bin/python3.2
$ pyenv which python
/home/yyuu/.pyenv/versions/2.7.3/bin/python

You can manage your version stack by pyenv push and pyenv pop.

$ pyenv local
2.7.3
3.2.3
$ pyenv push 3.3.0
$ pyenv local
2.7.3
3.2.3
3.3.0
$ pyenv pop
2.7.3
3.2.3

3.3 pyenv shell

Sets a shell-specific Python version by setting the PYENV_VERSION environment variable in your shell. This version overrides both project-specific versions and the global version.

$ pyenv shell pypy-1.9

When run without a version number, pyenv shell reports the current value of PYENV_VERSION. You can also unset the shell version:

$ pyenv shell --unset

Note that you'll need pyenv's shell integration enabled (step 3 of the installation instructions) in order to use this command. If you prefer not to use shell integration, you may simply set the PYENV_VERSION variable yourself:

$ export PYENV_VERSION=pypy-1.9

And also, you can specify multiple versions via PYENV_VERSION environment variable in your shell.

$ pyenv shell pypy-1.9 2.7.3
$ echo $PYENV_VERSION
pypy-1.9:2.7.3
$ pyenv version
pypy-1.9 (set by PYENV_VERSION environment variable)
2.7.3 (set by PYENV_VERSION environment variable)

3.4 pyenv versions

Lists all Python versions known to pyenv, and shows an asterisk next to the currently active version.

$ pyenv versions
  2.5.6
  2.6.8
* 2.7.3 (set by /home/yyuu/.pyenv/version)
  3.2.3
  jython-2.5.3
  pypy-1.9

3.5 pyenv version

Displays the currently active Python version, along with information on how it was set.

$ pyenv version
2.7.3 (set by /home/yyuu/.pyenv/version)

3.6 pyenv rehash

Installs shims for all Python binaries known to pyenv (i.e., ~/.pyenv/versions/*/bin/*). Run this command after you install a new version of Python, or install a gem that provides binaries.

$ pyenv rehash

3.7 pyenv which

Displays the full path to the binary that pyenv will execute when you run the given command.

$ pyenv which python3.2
/Users/sam/.pyenv/versions/3.2.3/bin/python3.2

3.8 pyenv whence

Lists all Python versions with the given command installed.

$ pyenv whence 2to3
2.6.8
2.7.3
3.2.3

4 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 file bugs on the issue tracker.

4.1 Version History

0.1.1 (September 3, 2012)

  • Support multiple versions of Python at a time.

0.1.0 (August 31, 2012)

  • Initial public release.

4.2 License

(The MIT license)

  • Copyright (c) 2011 Sam Stephenson
  • Copyright (c) 2012 Yamashita, Yuu

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.

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