I've heard about the PYTHONSTARTUP file as a way to automatically load specified modules and other code when starting python.  But PYTHONSTARTUP is a global thing, for all instances of python.  Is there such a thing as PYTHONSTARTUP that I can place in a specific directory and runs only when I start python in that directory?
This sounds like you want to use virtualenv. It's a tool for creating isolated python environments with hooks for individual settings. Just put them in the bin/activate of your virtualenv.
A PYTHONSTARTUP file for a specific directory