This is a pre-commit hook I use in my Python projects.

https://gist.github.com/3849310

Nevermind my feak bash-fu, in the end the script does what I want it to – the three following things:

• First, it checks if I haven’t forgotten to add a new module to the requirements.txt file. Most of the time this works like a charm with virtualenv and pip. The only drawback is installing modules in local experimental branches – these modules are not necessary in upstream branches and so they don’t belong to requirements.txt yet. When you switch back and want to commit in an upstream branch, the pre-commit hook fails. However, this is easily avoidable by using the --no-verify option of git commit.
• Second, it runs pyflakes on all the .py files in the repository. If there’s something pyflakes doesn’t like, the pre-commit hook fails and shows the output of pyflakes. There’s one case which is ignored and that is using the _ (underscore) function from the gettext module as install makes it available everywhere. Pyflakes documentation is non-existent and I guess there’s no way to create a configuration profile for it, so I had to resort to this hack.
• Finally, since I deployed code with forgotten set_trace() calls a couple of times, the third thing the script does is it checks for these and prints out the file and line number if it encounters any.

I keep this file as a part of the repository, making a symbolic link to it in .git/hooks/pre-commit. Make sure the file is executable.

Do you have similar stuff in your VCS hooks? Is there anything I could improve in mine? I’ll be glad to see your tips in the comments.