12 September 2010

Quiz Question

Say you have the following module code:

a = 1

class some_class:
    a = a

def some_function():
    a = a


What is going to happen? Well, think about it, the solution is in the next paragraph.


The correct answer is that the call “some_function()” is going to give you a “UnboundLocalError” exception.

This is because it in functions unlike in classes (or modules) do look ahead for assigned to variable names. Python allocates a slot for local variables of functions and that is a property that doesn’t change - unless you say “global” of course. This slot is used for every access to the variable name, which forbids you to make it local.

Surprised? I was too! I only learned it while doing my Python compiler Nuitka and I made it a separate posting, because it really surprised me how different function body and class body work.