🎯 What you will learn
- Read Python error messages
- Use print() to investigate bugs
- Handle errors with try/except
👋 Let’s get started!
Error messages aren’t scary — they’re clues! 🕵️ Pro coders spend lots of time debugging. Learn their tricks and you’ll fix bugs in seconds.
🪜 Step by step
1. 📜 Read the error
The last line tells you the error type and message. The line number tells you where.
print("Hello)
# SyntaxError: unterminated string literal2. 🔦 Print debugging
Add print() lines to see what your variables really contain.
total = 0
for n in [1, 2, 3]:
total = total + n
print("n =", n, "total =", total)3. 🛡️ try / except
Catch errors so your program doesn’t crash.
try:
age = int("twelve")
except ValueError:
print("Please type a number like 12")🧪 Try it!
Change the code and press ▶ Run to see what happens. You can’t break anything!
Safe divider
def safe_divide(a, b):
try:
return a / b
except ZeroDivisionError:
return "Can't divide by zero! 🙅"
print(safe_divide(10, 2))
print(safe_divide(5, 0))Catch a bad answer
answer = "seven"
try:
number = int(answer)
except ValueError:
print("That is not a number!")📖 Key words
Tap a card to flip it over!
- Error message
- Python’s clue about what went wrong 📜
- Traceback
- The trail showing where the error happened 👣
- try/except
- Catches errors so the program keeps going 🛡️
🏆 Challenge
This code has 2 bugs. Fix them so it prints: Total: 15
Challenge
numbers = [5, 5, 5]
total = 0
for n in numbers
total = total + n
print("Total: " + total)Knowledge Check Quiz
- Which error happens here?
- What does except do?
- Best first step when you see an error?