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Converting invalid text to a number
🐛 Fix the bug Topic: strings Difficulty: medium Free
What this problem practises
Python strings are immutable sequences. "Fixing" a string always produces a new one, so the return value has to be captured; slicing rules apply, and every method — upper(), strip(), split(), join() — behaves differently from the in-place mutation you might be picturing.
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 convert user input into a number and double it, but it crashes on certain input. 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: ValueError: invalid literal for int() with base 10: 'twenty'. 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:
age_text = "twenty"
age = int(age_text)
print(age * 2)More strings problems
Keep going
- Python debugging guide — a systematic method for finding bugs like this one fast.
- Browse every strings problem in this topic.
- Common Python errors and what they actually mean, plus the Python glossary for any term used on this page.