Virtualenv and Setuptools
Portion of my time at Anomaly is spent conceiving tools and processes that make us (and hopefully other developers) do our jobs that little bit better. We built and maintain a Python REST micro framework which is at the heart of all of our recent work. We've been working on a couple more developer for developer tools that we intend to release later this year.
Python is our programming language of choice. Amongst many very talented developers who author and maintain various Python projects that we depend on daily, I'm a big fan of the work of Armin Ronacher and the guys at Pocoo.
I came across Armin's thoughts on Setuptools Integration while trying to streamline our development and deployment process for Python applications (we use Click for several of our projects).
Using Virtualenv in editable mode sandboxes your application's Python environment and as Armin puts it "makes Python development sane".
$ virtualenv venv $ . venv/bin/activate $ pip install --editable .
If you're a Python developer and haven't already, I highly encourage all Python developers to investigate Virtualenv and Setuptools.