Modifying a variable before it's assigned locally

What this problem practises

Function bugs are mostly about names and values: positional argument order, default parameters evaluated once at definition time, local versus global scope, and the implicit None returned whenever a function has no return.

This is a fix-the-bug problem: a short program is given in its broken state, and the task is to repair the code so it produces the required output. The interactive editor runs your fixed version in the browser and checks it for you — no setup, no local interpreter.

Difficulty: medium — expect to hold two interacting rules in your head at once, such as a boundary combined with a mutation.

The challenge

This should increase a counter and print it, but crashes. Fix it.

The code runs in PyDebug’s in-browser compiler. Open the problem, run the snippet, watch the exact error or output, and keep iterating until it is right. Signed-in solves count toward XP and your daily streak.

The error it raises

Run the broken snippet and Python stops with this exact error: UnboundLocalError: local variable 'count' referenced before assignment. Match it to the Python errors guide, then repair the line that produced it — knowing the message is half the fix.

The snippet

The interactive editor pre-fills exactly this code, broken and ready to repair:

count = 0

def increment():
    count += 1
    print(count)

increment()

More functions problems

• abs() and type conversion easy
• Operator precedence easy
• Mutable default argument trap medium

Keep going

• Python debugging guide — a systematic method for finding bugs like this one fast.
• Browse every functions problem in this topic.
• Common Python errors and what they actually mean, plus the Python glossary for any term used on this page.