For example if I have a package foo that's already on Pypi. I want to be able to git push origin master with a new version number in my setup.py, and then Pypi somehow auto updates their version/source code. Is this possible? If not is there some similar workflow that someone could share? This is my first time contributing to Pypi and I want to make the experience as easy going as possible.
I think the behaviour you're after would be best developed using git hooks. I'm not entirely sure that's the best rabbit hole to go down though, but here's some information if you're interested. (Publishing to Pypi automatically without additional checks could lead to your package being unreliable for other users!)
If you are pushing to PyPI, I assume you are developing an Open Source package? If you are, why not make use of the free CI tool Travis to run your tests and other CI tasks. One of your tasks could be to automatically upload your package to PyPI on successful new builds.