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pyenv /pyenv

Simple Python version management

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Simple Python Version Management: pyenv

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Build Status

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 andruby-build, and modified for Python.

Terminal output example

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 virtualenvyourself, or pyenv-virtualenvto 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
    PATH
    for an executable file named
    pip
  • Find the pyenv shim named
    pip
    at the beginning of your
    PATH
  • 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:

  1. The

PYENV\_VERSION

environment variable (if specified). You can use the [

pyenv shell

](https://github.com/pyenv/pyenv/blob/master/COMMANDS.md#pyenv-shell) command to set this environment variable in your current shell session. 2.

The application-specific

.python-version

file in the current directory (if present). You can modify the current directory's

.python-version

file with the [

pyenv local

](https://github.com/pyenv/pyenv/blob/master/COMMANDS.md#pyenv-local)command. 3.

The first

.python-version

file found (if any) by searching each parent directory, until reaching the root of your filesystem. 4.

The global

$(pyenv root)/version

file. You can modify this file using the [

pyenv global

](https://github.com/pyenv/pyenv/blob/master/COMMANDS.md#pyenv-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 your

PATH

.)

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

Homebrew on macOS

  1. Consider installing with Homebrew
    sh brew update brew install pyenv
  2. Then follow the rest of the post-installation steps under Basic GitHub Checkout, starting with #3 ("Add
    pyenv init
    to your shell to enable shims and autocompletion").

If you're on Windows, consider using @kirankotari's [

pyenv-win

](https://github.com/pyenv-win/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 ~/.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 the 

pyenv

 command-line utility.

- For **bash**: ~~~bash echo 'export PYENV_ROOT="$HOME/.pyenv"' \>\> ~/.bash_profile echo 'export PATH="$PYENV_ROOT/bin:$PATH"' \>\> ~/.bash_profile~~~

- For **Ubuntu Desktop**: ~~~bash echo 'export PYENV_ROOT="$HOME/.pyenv"' \>\> ~/.bashrc echo 'export PATH="$PYENV_ROOT/bin:$PATH"' \>\> ~/.bashrc~~~

- For **Zsh**: ~~~zsh echo 'export PYENV_ROOT="$HOME/.pyenv"' \>\> ~/.zshrc echo 'export PATH="$PYENV_ROOT/bin:$PATH"' \>\> ~/.zshrc~~~

- For **Fish shell**: ~~~fish 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_proxy

 and 

HTTPS_PROXY

 too.

1. 

**Add 

pyenv init

 to 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 

PATH

 during the initialization.

sh echo -e 'if command -v pyenv 1>/dev/null 2>&1; then\n eval "$(pyenv init -)"\nfi' >> ~/.bash_profile


  - **Zsh note**: Modify your 

~/.zshrc

 file instead of 

~/.bash_profile

.
  - **fish note**: Use 

pyenv init - | source

 instead of 

eval (pyenv init -)

.
  - **Ubuntu and Fedora note**: Modify your 

~/.bashrc

 file instead of 

~/.bash_profile

.

**General warning**: There are some systems where the

BASH_ENV

 variable is configured to point to 

.bashrc

. On such systems you should almost certainly put the above mentioned line

eval "$(pyenv init -)"

 into 

.bash_profile

, and **not** into 

.bashrc

. Otherwise you may observe strange behaviour, such as 

pyenv

 getting into an infinite loop. See [#264](https://github.com/pyenv/pyenv/issues/264) for details.
2. 

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

sh exec "$SHELL"

3. [**Install Python build dependencies**](https://github.com/pyenv/pyenv/wiki#suggested-build-environment) before attempting to install a new Python version.

4. 

**Install Python versions into 

$(pyenv root)/versions

.** For example, to download and install Python 2.7.8, run:

sh pyenv install 2.7.8

**NOTE:** If you need to pass configure option to build, please use

CONFIGURE_OPTS

 environment variable.

**NOTE:** If you want to use proxy to download, please use

http_proxy

 and 

https_proxy

 environment variable.

**NOTE:** If you are having trouble installing a python version, please visit the wiki page about [Common Build Problems](https://github.com/pyenv/pyenv/wiki/Common-build-problems)

#### Upgrading

If you've installed pyenv using homebrew, upgrade using:

sh 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.

1. To **disable** pyenv managing your Python versions, simply remove the

pyenv init

 line from your shell startup configuration. This will remove pyenv shims directory from PATH, and future invocations like

python

 will 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.
1. 

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:

sh 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:
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 root)/shims

 to your 

$PATH

.
2. 

**Installs autocompletion.** This is entirely optional but pretty useful. Sourcing

$(pyenv root)/completions/pyenv.bash

 will set that up. There is also a 

$(pyenv root)/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.

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.

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](https://github.com/pyenv/pyenv/blob/master/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

](https://github.com/pyenv/pyenv/blob/master/COMMANDS.md#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

PYENV_HOOK_PATH

 | [_see wiki_](https://github.com/pyenv/pyenv/wiki/Authoring-plugins#pyenv-hooks) | 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

](https://aria2.github.io/).  
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](https://github.com/pyenv/pyenv). It's clean, modular, and easy to understand, even if you're not a shell hacker.

Tests are executed using [Bats](https://github.com/bats-core/bats-core):

bats test bats/test/.bats

```

Please feel free to submit pull requests and file bugs on the issue tracker.

Version History

See CHANGELOG.md.

License

The MIT License

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