Two options in setup.py
python setup.py install
python setup.py develop
python setup.py install is used to install (typically third party) packages that you're not going to be developing/editing/debugging yourself.
For your own stuff, you want to get your package installed and then be able to frequently edit your code and not have to re-install your package—this is exactly what
python setup.py develop does: installs the package (typically just a source folder) in a way that allows you to conveniently edit your code after its installed to the (virtual) environment and have the changes take effect immediately.