Mutable Functions

• functions with behavior that changes over time

• oposite of a "pure" or "deterministic" function

NONLOCAL

• mutable values can be changed without a nonlocal statement (b[0] = new_value)

• modify a binding in a parent frame instead of just looking it up

• a variable declared nonlocal must:

  • exist in a parent frame

  • not exist in the current frame