pythonScope errorMedium

Label maker says str is not callable

Time: 0:00

BugFind the bug and fix the code

What it should do

make_label(text, number) builds an order label. Example: make_label("Order", 5) → "Order #5".

What happens instead

make_label("Order", 5) crashes: TypeError: 'str' object is not callable.

def make_label(str, number):
    return str + " #" + str(number)

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

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This bug belongs to the scope and closure bugs pattern

Every callback reports the last value, a counter never increments, UnboundLocalError on a variable you can see.

Learn the scope and closure bugs pattern Step through your own code

Spoiler: why this bug happens(try it first; the hints get warmer one at a time)

What went wrong: the parameter is named str. Inside the function, str is now the text "Order", so str(number) tries to call text like a function.

The fix: def make_label(text, number): return text + " #" + str(number)

Remember: don't name variables str, list, dict, sum, max, min or input.

The pattern behind it: scope and closure bugs.

More scope and closure bugs to practise

Seen this error in your own code?

TypeError: 'list' object is not callable TypeError: 'str' object is not callable

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