12 July 2013

virtualenv is a pretty awesome tool for any python user, however it is often too easy to accidentally install new packages into the wrong place. Here I show you how to separate your system packages and that of your project environments.

Intro

Jump "straight" to the Syspip section if you know all about python packaging and virtualenv.

virtualenvwrapper

This is a really useful tool, even if it adds binaries with amazingly long names. It lets you easily and quickly list, add, and switch to a virtualenv.

I don't usually need all the many options this script provides, and would also prefer for it to be easier to combine the virtualenvwrapper's and git's PS1 prompt changes.

Changing Environments

To change environments is pretty easy, you just use the workon command. This works whether you have a currently active environment or not.

workon $env_name

To deactivate the current environment you use the deactivate command, just like normal. Though personally I though workoff was more obvious.

alias workoff=deactivate

Tab Completion!

When using the workon command you can tab complete to see the list of all the environments you have.

Add/Remove Environments

# Add a new environment
mkvirtualenv $env_name

# Remove an environment
rmvirtualenv $env_name

Syspip

Heres where stuff gets interesting. To prevent mistakes while installing packages, I've added the following things to my bash startup scripts (.bashrc, .bash_aliases, etc.)

# .bashrc

source /usr/local/bin/virtualenvwrapper.sh

export WORKON_HOME=$HOME/.environments
export PIP_VIRTUALENV_BASE=WORKON_HOME

export PIP_REQUIRE_VIRTUALENV=true

First notice that we set PIP_REQUIRE_VIRTUALENV, this ensures that pip will not run without an active virtual environment.

Second, do remember to set PIP_VIRTUALENV_BASE, since that is what pip uses to tell if you have an environment active. (AFAIK)

# .bash_aliases

export SYSTEM_PIP=`which pip`
function syspip {
    PIP_REQUIRE_VIRTUALENV="" sudo $SYSTEM_PIP "$@"
}

Here we first find which version of pip we use, then add a new way of using the global pip binary. Now you have 2 ways of installing a package, each of which always installs to the expected location.

To install only for the currently active environment, (or fail if it doesn't find one)
```
pip install $package
```
To install only globally
```
syspip install $package
```

Don't forget to load .bash_aliases before you activate any environments, otherwise syspip might not work as advertised.

Saevon

Python Virtual Environments and PIP Keep your projects separate.