🐞 Debugging Errors

🐍 Python Debugging Process

Code not working? Follow the steps in the debugging process below before asking a peer or your teacher! Fixing your own errors, no matter how small, is one of the best ways to become a better coder.

Read the Error Message
- Look at the bottom line of the traceback — that’s the actual error type (e.g., NameError, IndentationError, TypeError).
- Read the line number the error happened on and the line above it, too.
Check Your Spacing and Indentation
- Make sure every indent is exactly 4 spaces, not tabs.
- Blocks like if, for, while, def, and class must be followed by a colon (:) and indented on the next line.
- Every nested block should line up vertically.
Check Your Capitalization
- Python is case-sensitive. print, Print, and PRINT are all different!
- Be consistent with how you spell variable names, functions, and keywords.
Check Spelling and Naming
- Misspelled variable? Function name? Python won’t guess — you must match exactly.
- Watch for typos like pritn instead of print.
Check Symbols and Syntax
- Strings must be inside quotes: "Hello" or 'Hi'
- Use == for comparison, not =
- Colons (:) after if, for, while, def, and class
- Matching parentheses (), brackets [], and braces {}
Print Often
- Add print() statements to check what your variables contain.
- Print just before the line that crashes to see what’s going on.
Run Small Pieces at a Time
- Don’t write 50 lines and then run. Test after every few lines.
- Break big problems into small chunks and test each one.
Use Meaningful Variable Names
- This makes it easier to track your logic and avoid confusion.
Ask Yourself Questions
- What is this line trying to do?
- What type is this variable? (int, str, list…)
- Should this function return something? Is it?
If All Else Fails…
- Comment out sections of your code and slowly re-enable them.
- Use a visualization tool like PythonTutor.com to “step through” code, which shows what’s happening line-by-line.