Managing Python libraries across git projects

March 01, 2011

I finally got around to nuking from orbit cleaning up my virtual machine. Maybe this time around I can make it a whole year without wrecking all the permissions on $HOME (I once had to sudo ls…no joke).

I know that all good Python comrades should be using pip for installing packages and virtualenv for managing them per project, but I never really got into the latter. I was pretty lazy and just shoved everything into the global site-packages, but since I had a fresh start I decided to do it The Right Way™ this time.

And man, is it awesome!

There is a sweet wrapper for virtualenv that I didn’t find (exist?) last time I tried to get this setup working. virtualenvwrapper makes it less painful to manage multiple environments and has a super neat hook system.

And then I found a handy bash script to automatically switch your environments when you cd to a git repo.

Here is my new workflow:

matt@nigiri:~$ mkvirtualenv foo-project
matt@nigiri:~$ mkdir projects/foo-project/ && cd projects/foo-project/

(foo-project)matt@nigiri:~/projects/foo-project$ git init
(foo-project)matt@nigiri:~/projects/foo-project$ pip install flask   

Flask is only installed into this environment, if you open a python shell inside foo-project you can import the module, but if you cd out to $HOME and try you will get an ImportError.

pip freeze > requirements.txt   

Now you can enumerate the project dependancies (including versions) so that when someone clones the project they can install them all in one-go.

(foo-project)matt@nigiri:~/projects/foo-project$ cd
matt@nigiri:~$  

Once you leave the repository folder, your environment is automatically deactivated. Then, when you go to work on foo-project again – it will be reactivated when you cd in.

It’s pretty slick. If you want more info, check out:
http://mathematism.com/2009/07/30/presentation-pip-and-virtualenv/

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