REQUIREMENTS files.

Seriously, I use this in conjunction with virtualenv every day.

QUICK DEPENDENCY MANAGEMENT TUTORIAL, FOLKS

Requirements files allow you to create a snapshot of all packages that have been installed through pip. By encapsulating those packages in a virtualenvironment, you can have your codebase work off a very specific set of packages and share that codebase with others.

From Heroku's documentation https://devcenter.heroku.com/articles/python

You create a virtual environment, and set your shell to use it. (bash/*nix instructions)

virtualenv env source env/bin/activate

Now all python scripts run with this shell will use this environment's packages and configuration. Now you can install a package locally to this environment without needing to install it globally on your machine.

pip install flask

Now you can dump the info about which packages are installed with

pip freeze > requirements.txt

If you checked that file into version control, when someone else gets your code, they can setup their own virtual environment and install all the dependencies with:

pip install -r requirements.txt

Any time you can automate tedium like this is awesome.