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Error Handling – try/except basics

A try/except block runs code and catches errors so the program does not crash

Part of: Python Coding — Module 22, VCE Software Development - U3O1 - Programming — Module 120, VCE Software Development - U4O1 - development and evaluation — Module 141, 9-10 Digital Technologies: Object-oriented programming, debugging and testing — Module 10, VCE Applied Computing U1O2 Programming: Validating data — Module 3, ACARA Digital Technologies Years 9–10 — Testing and Validating Programs — Module 47, QCE Digital Solutions Unit 2 — Prototype Data Solutions — Module 70, QCE Digital Solutions Unit 4 — Prototype Digital Data Exchanges — Module 36, WA Computer Science ATAR Year 11 — Control Structures and Data Types — Module 71

Understanding Error Handling – try/except basics in Python

What it does: Naming the exception type catches only that specific kind of error. try/except intercepts errors and lets you handle them gracefully. Put risky code inside try — if it fails, except handles it. If try succeeds, except is completely skipped. int('abc') causes a ValueError — except catches it and prints 'Oops'. 5 + 3 works fine — no error, so except is skipped. 'hello' can't be converted to an integer — that's a ValueError. except always needs a matching try block before it.

Common mistakes: Missing colon after try. Missing colon after except.

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This module's key terms are also in a printable crossword (Modules 21–30) and word search (Modules 21–40).

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Learning
Duo
What does try/except do?
Catches errors so the program doesn't crashMakes code faster
Matches
❌ try: x = int('abc') exept: print('oops')
↓
Error: Typo — 'except' not 'exept'
Applying
Meanings
Term
try
Meaning
Block containing code that might cause an error.
Practice
try:
Testing
Gaps
:
Check Answer
Spots
1try
2 num = int(input('Number: '))

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Quick Questions

1. What does try/except do?
A. Catches errors so the program doesn't crash ✓
B. Makes code faster
try/except intercepts errors and lets you handle them gracefully
2. What goes inside the try block?
A. Error messages
B. Code that might cause an error ✓
Put risky code inside try — if it fails, except handles it
3. When does the except block run?
A. Always
B. Only when an error occurs in try ✓
If try succeeds, except is completely skipped
4. try:\n int('abc')\nexcept:\n print('Oops')\nWhat prints?
A. Oops ✓
B. abc
int('abc') causes a ValueError — except catches it and prints 'Oops'
5. try:\n print(5 + 3)\nexcept:\n print('Error')\nWhat prints?
A. 8 ✓
B. Error
5 + 3 works fine — no error, so except is skipped

Match the Pairs

try: x = int('abc') exept: print('oops') → Error: Typo — 'except' not 'exept'
except: print('error') try: risky() → Error: try must come before except
try: x = int(val) except ValueError: print('bad') → Valid: Catches ValueError only
try: risky() except: print('handled') → Ok: Catches any error
try: print(int('hi')) except: print('error') → Output: error
try: print(int('5')) except: print('error') → Output: 5

Key Term

try
Block containing code that might cause an error.~~except

Fill in the Blanks

1. try: num = int(input('Number: ')) except: print('Invalid')
2. try: num = int(input('Number: ')) except: print('Invalid')
3. try: num = int(input('Number: ')) except ValueError: print('Not a number')
4. try: result = 10 / 0 except: print('Error')
5. try: x = int(input('Enter num: ')) except: print('Bad input')

Spot the Error

Question 1
A try
B num = int(input('Number: '))
C except:
D print('Invalid')
Line A — Missing colon after try
Question 2
A try:
B num = int(input('Number: '))
C except
D print('Invalid')
Line C — Missing colon after except
Question 3
A try:
B num = int(input('Number: '))
C except:
D print('Invalid')
Line B — Code inside try must be indented
Question 4
A except:
B print('Invalid')
C print('Try again')
D print('Done')
Line A — except cannot stand alone: it must follow a try block
Question 5
A Try:
B num = int('abc')
C Except:
D print('Error')
Line A — try and except must be lowercase

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