I have done nothing, and everything is broken.
aviv$ python3 -c \'import setuptools\' Traceback (most recent call last): File \"/usr/lib/python3.5/pkgutil.py\"
Found the answer — it's really stupid.
I was trying to run everything from a directory that no longer existed. os.getcwd() itself was erroring out. Changed directories, ran again, works now.
os.getcwd()