Interfaces above and below were well-specified
Internal interfaces were in flux
"Understand one level of abstraction below the one you normally work at."
"Have ready access to the layer of abstraction below you."
"The power of successive refinement and iterative development. Impossible without continuous aggressive refactoring." - Uncle Bob Martin
Screen-space constraints forced me to write smaller functions, classes, etc.
Fast iteration helped me mercilessly refactor.
Final, working code was there at the end
pip install --use-wheel ipython pyzmq jinja2 tornado