envplus

Combine your Python virtualenvs into unlimited configurations.

Developed at BuzzFeed.

Why Combine Virtualenvs?

Most of my projects are modular in nature. Yours probably are too. The large bulk of my projects involve some combination of:

Web-scraping and data-fetching
Data analysis
Web development

For each of these tasks, I've found a set of Python libraries that fit my needs well. Rather than download and install SciPy for the nth time, wouldn't it be nice just to build on top of already-installed versions? Enter envplus.

How It Works

envplus takes advantage of Python's .pth file convention. It creates (and manipulates) a special file, _envplus.pth, in the site-packages directory of your current virtualenv.

Installation

pip install envplus

Walkthrough

If you're like me, a lot of your projects involve fetching and parsing web pages. So let's build a virtualenv that contains a handy trio of packages for this task.

mkvirtualenv scraping
pip install requests
pip install lxml
pip install cssselect

For a lot of projects, you'll probably also want to store information in some sort of database. Let's make a bare-bones virtualenv for this task, too.

mkvirtualenv dbstorage
pip install dataset

Now let's say you're working on a project to scrape cat GIFs from BuzzFeed and store them in a database. Rather than reinstall all the packages above, you can just do this:

mkvirtualenv buzzcats
envplus add scraping dbstorage

Now you can use requests, lxml, cssselect, and dataset in your buzzcats virtualenv. The actions you take in the buzzcats virtualenv will not harm or alter your other virtualenvs. (Even if you run pip uninstall.) And upgrades to scraping and other envplus add'ed virtualenvs will become immediately available to buzzcats.

Usage

To use envplus, virtualenvwrapper must be installed and your target virtualenv must be currenlty activated.

envplus add [envs]

Make another virtualenv's packages available to your current virtualenv. Accepts multiple, space-separated virtualenv names.

envplus add scraping dbstorage

envplus rm [envs]

Remove a previously added virtualenv from your current virtualenv. Accepts multiple, space-separated virtualenv names.

envplus rm scraping dbstorage

envplus pause [envs]

"Pauses" previously added virtualenvs, so that they remain in _envplus.pth (as commented lines) but do not effect the current virtualenv. If virtualenv names are provided, only those are paused. Otherwise, all previously added virtualenvs are paused.

# To pause all
envplus pause
# To pause just one
envplus pause dbstorage

envplus resume [envs]

Un-pauses previously added virtualenvs. If virtualenv names are provided, only those are resumed. Otherwise, all previously added virtualenvs are resumed.

# To resume all
envplus resume
# To resume just one
envplus resume dbstorage

envplus ls [-p] [-a]

List added virtualenvs. By default, lists only non-paused additions. -p will list only paused additions, and -a will list all additions.

envplus run [command]

Temporarily adds your virtualenvs' bin-paths to your current PATH before running command. Lets you use other virtualenvs' command-line programs.

# Create a dummy virtualenv with csvkit
mkvirtualenv csvtest
pip install csvkit

# Create newenv and add csvtest
mkvirtualenv newenv
envplus add csvtest

# While in newenv, run csvkit's csvcut command-line utility
echo "a,b,c" | envplus run csvcut -c 2

envplus path

Print the path of the active virtualenv's _envplus.pth file.

envplus path

envplus cat

Print the contents of the active virtualenv's _envplus.pth file.

envplus cat

envplus edit

Open the active virtualenv's _envplus.pth file in your default editor. You probably shouldn't do this. Mostly for debugging purposes.

envplus edit

Todos

Add tests.
Test on wider variety of systems and virtualenv(wrapper) versions.

jsvine/envplus