Structure:

.
├── setup.py
└── src
    └── my_topology
        ├── __init__.py
        └── __main__.py

• setup.py provides data for packaging up the files under it into a python package
• __init__.py is so that src/my_topology/ is discovered as a python package.
• __main__.py is like the if __name__ == "__main__": thing in python, but in its own file so you can run the parent module (my_topology instead of a submodule e.g. my_topology.entrypoint if that if was in a my_topology/entrypoint.py)

To build these into a pex, you can do

cd "$top_directory"
pex \
    --python=python3 \
    --entry-point=my_topology \
    --output=my_topology.pex \
    .
heron submit my_topology.pex -

Trivia:

• a pex is a zip file, so you can inspect the contents to see your packaged files, e.g. unzil -l my_topology.pex | grep my_topology
• a pex can be executed (thanks to python executing zip files [e.g. "eggs"]) e.g. ./my_topology.pex (what heron can do internally to get data about the topology)