I am developing a library and an application that uses the library in Python 2.6.  I've placed a "mylib.pth" file in "site-packages" so that I can import mylib from within my application.  
I am using a DVCS so when I want to fix a bug or add a feature to the library I make a branch of the repository and work within that branch.  To test my application with the changes I am making to the library I edit the path in "mylib.pth" to point to the new development branch.
This gets a little tedious if I have a few parallel branches of my library going on at one.  I have to keep editing the "mylib.pth" file before testing to ensure I am testing against the correct version of my library.  Is there a way to use the current path (i.e. the development branch of the library that I am current in) to set the library path when I invoke my application instead of using the "mylib.pth" in the global "site-packages" directory?
If you use setuptools, then you can say setup.py develop in your working tree, and it will do the .pth file manipulation for you.
Setting Python path while developing library module