14.8. Function Gotchas

Here are some of the more jagged edges of functions you might not expect. They're all obscure, and a few have started to fall away from the language completely in recent releases, but most have been known to trip up a new user.

14.8.1. Local Names Are Detected Statically

Python classifies names assigned in a function as locals by default; they live in the function's scope and exist only while the function is running. What we didn't tell you is that Python detects locals statically, when it compiles the def's code, rather than by noticing assignments as they happen at runtime. This leads to one of the most common oddities posted on the Python newsgroup by beginners.