Debugging

301.13 Testing

Testing — Note 6 of 6

Find and fix logic errors.

What you need to know

Debugging is the process of finding and fixing errors. Syntax errors are caught by Python, but logic errors produce wrong results and must be found by testing and tracing.

What to know

Syntax error: code won't run (e.g. missing colon)
Logic error: code runs but gives wrong answer
Use print() statements to check variable values
Use a trace table to find where logic goes wrong
Fix the bug, then re-test to confirm

Code examples

Debugging with print

python

def average(a, b):
    total = a + b
    print("DEBUG: total=" + str(total))  # temporary
    avg = total / 2
    return avg

print(average(10, 20))  # DEBUG: total=30 → 15.0

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Specification notes for programming are in Paper 2.