My first car was a Volkswagen Golf and I was in love with it. It had dark metallic paint, a stereo set loud enough to vibrate the windows and the biggest wheels money could buy. This car was perfect! It only had one flaw. It shut off its engine at traffic lights.
So I went back to the car dealer. The first thing they did, was replacing the fuse box. The problem was solved! At the first traffic light, the engine shut off again. Back to the garage. This time, they tweaked every board computer setting. The problem was solved!
But you guessed it... At the first traffic light, the engine shut off. After 8 visits and a new board computer, the problem still was not fixed. And then it happened...
While 5 young mechanics stood around the running engine, an older mechanic walked by and said: This car is gasping for air. What? Five dimpled faces looked confused at the old guy. "Here!", he said, and sprayed something on a tube. And what do you know, there was a leakage!
Now of course it was not the 3$ spray that fixed the problem. It was one guy's experience that lead him to look beyond the modules in the system. Just by listening to the car, he knew what tiny part of the car caused the problem.
The Python Type System is much like an engine. When it works, nobody thinks about it. But it needs to be fine-tuned. Small details can have major impact on the system.