This is more of a tox question, but if i'm using tox to invoke pex as a packaging step, is there a way I can pass into pex the requirements that's defined in a setup.py script?

No. You can, however say

pex <dir containing setup.py> -o my_setup_py_project_packaged_as_a_pex.pex

. Pex will then run your

setup.py

in an isolated chroot both resolving its requirements and building your own dist and packaging all this in a pex.

woof! this is the info i needed 😄