pyenv

multiple Python environments

Matias Guijarro, matias.guijarro@free.fr

PUG Grenoble, 22/10/2015

Introduction

So many Pythons...

CPython 2.x, CPython 3.x, PyPy, Jython, Anaconda, ...

What if you need more than 1 Python ?

Usecase 1: Python 2.7 for legacy projects, Python 3 for new ones
Usecase 2: CPython for common projects, PyPy for specific ones
Usecase 3: OS-installed Python has to stay untouched in the system, but you need a more recent version

... here comes the need for a standalone Python versions manager

pyenv

Fork of rbenv by Yuu Yamashita

pyenv

pyenv lets you easily switch between multiple versions of Python

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

Just Unix shell scripts !

Does not depend on Python itself
caveat: Doesn't work on Windows (Cygwin is ok)

pyenv

How it works ?

inserts a shims directory in front of PATH

Note: In computer programming, a shim is a small library that transparently intercepts API calls and changes the arguments passed, handles the operation itself, or redirects the operation elsewhere.

intercepts Python commands and redirect them to the right executable according to the required Python version

$ echo $PATH
/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin

# use pyenv first
$ echo $PATH
~/.pyenv/shims:~/.pyenv/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin

pyenv

Choosing the Python version

PYENV_VERSION environment variable
.python-version file in application directory
global ~/.pyenv/python-version file

pyenv

pyenv does not automatically create shims for

new executables after installation

use "pyenv rehash" command

pyenv installation

matias@kashyyyk:~$ git clone https://github.com/yyuu/pyenv.git ~/.pyenv
Cloning into '/home/matias/.pyenv'...
[...]
Checking connectivity... done.

Add pyenv init to the shell to enable shims and autocompletion

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

Define PYENV_ROOT environment variable and add PYENV_ROOT/bin to PATH to get access to pyenv utility

Clone repository

matias@kashyyyk:~$ echo 'eval "$(pyenv init -)"' >> ~/.bash_profile

Reload .bash_profile

matias@kashyyyk:~$ source ~/.bash_profile

pyenv usage

matias@kashyyyk:~$ pyenv install 3.4.3
Downloading Python-3.4.3.tgz...
-> https://yyuu.github.io/pythons/4281ff86778db65892c05151d5de738d
Installing Python-3.4.3...
WARNING: The Python bz2 extension was not compiled. Missing the bzip2 lib?
Installed Python-3.4.3 to /home/matias/.pyenv/versions/3.4.3

matias@kashyyyk:~$ pyenv versions
* system (set by /home/matias/.pyenv/version)
  3.4.3
matias@kashyyyk:~$

List installed versions

Install a Python version

pyenv usage

Switching between Python versions

matias@kashyyyk:~$ python
Python 2.7.6 (default, Jun 22 2015, 17:58:13) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 
matias@kashyyyk:~$ pyenv shell 3.4.3
matias@kashyyyk:~$ python
Python 3.4.3 (default, Oct 21 2015, 23:47:55) 
[GCC 4.8.4] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 
matias@kashyyyk:~$ which pip
/home/matias/.pyenv/shims/pip
matias@kashyyyk:~$