Unexpected Behavior

Welcome to the unexpected Python behavior guide. This section collects language behaviors that often surprise people at first, especially around mutability, identity, imports, defaults, and truthiness.

Unexpected behavior

Work through these topics in order to build a clearer mental model of how Python behaves in edge cases and confusing situations.

Closures in Loops

Shallow vs Deep Copies

Mutable Defaults

dict.get() - Missing vs None

Exception Handler Order

Float Comparisons

Avoid import *

Identity vs Equality

Mutating While Iterating

Repeated Nested Lists

sort() vs sorted()

Truthiness and Missing Values