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Error Handling – try/except basics

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

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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Learning

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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. Only when an error occurs in try ✓

B. Always

If try succeeds, except is completely skipped

4. try:\n int('abc')\nexcept:\n print('Oops')\nWhat prints?

A. abc

B. Oops ✓

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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