Handling specific exceptions in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of handling specific exceptions in Python?

Handling specific exceptions allows your program to respond differently to different error types, making your code more robust and easier to debug.

beginner

How do you catch a specific exception in Python?

Use a try-except block and specify the exception type after except, like:

try:
    # code
except ValueError:
    # handle ValueError

intermediate

What happens if you catch a general exception instead of a specific one?

Catching a general exception (like Exception) can hide bugs and make it harder to find the real problem because it catches all errors, not just the ones you expect.

intermediate

Can you handle multiple specific exceptions in one except block? How?

Yes, by using a tuple of exception types after except, like:

except (TypeError, ValueError):
    # handle both exceptions

intermediate

What is the role of the else clause in try-except blocks?

The else clause runs code only if no exceptions were raised in the try block. It helps separate normal code from error handling.

Which syntax correctly catches a ZeroDivisionError in Python?

A try: ... except error ZeroDivisionError: ...

B try: ... catch ZeroDivisionError: ...

C try: ... except ZeroDivisionError: ...

D try: ... except: ZeroDivisionError ...

In Python, you catch specific exceptions using 'except ExceptionType:', so option C is correct.

What will happen if you write 'except:' without specifying an exception?

A It catches all exceptions.

B It catches only syntax errors.

C It causes a syntax error.

D It catches no exceptions.

An except block without an exception type catches all exceptions, which can hide bugs.

How do you handle both ValueError and TypeError in one except block?

A except ValueError & TypeError:

B except ValueError or TypeError:

C except ValueError, TypeError:

D except (ValueError, TypeError):

Use a tuple of exceptions in parentheses after except to catch multiple types.

What is the purpose of the else clause in a try-except block?

A Runs code only if an exception occurs.

B Runs code only if no exception occurs.

C Runs code before the try block.

D Runs code after finally block.

The else clause runs only if the try block did not raise any exceptions.

Why is it better to catch specific exceptions rather than all exceptions?

A To handle errors more precisely and avoid hiding bugs.

B To hide bugs.

C To avoid writing except blocks.

D To make the program slower.

Catching specific exceptions helps handle errors properly and keeps bugs visible.

Explain how to handle multiple specific exceptions in Python and why it is useful.

Think about grouping exceptions in one except block.

Describe the role of the else clause in a try-except block and when you would use it.

It runs only when the try block succeeds.

Practice

1. What is the main purpose of using try-except blocks in Python?

easy

A. To catch and handle specific errors so the program doesn't crash

B. To speed up the program execution

C. To write comments inside the code

D. To create new functions automatically

Solution

1. Step 1: Understand the role of try-except

   The try-except block is used to catch errors that happen during program execution.

2. Step 2: Identify the benefit of catching errors

   By catching errors, the program can handle them gracefully and continue running instead of crashing.

3. Final Answer:

   To catch and handle specific errors so the program doesn't crash -> Option A

4. Quick Check:

   try-except = catch errors [OK]

Hint: Try-except blocks catch errors to avoid crashes [OK]

Common Mistakes:

• Thinking try-except speeds up code
• Confusing try-except with comments
• Believing try-except creates functions

2. Which of the following is the correct syntax to catch a ZeroDivisionError in Python?

easy

A. try:
x = 1/0
except:
print('Error')

B. try:
x = 1/0
catch ZeroDivisionError:
print('Cannot divide by zero')

C. try:
x = 1/0
except ZeroDivisionError:
print('Cannot divide by zero')

D. try:
x = 1/0
except ZeroDivision:
print('Cannot divide by zero')

Solution

1. Step 1: Check the correct keyword for catching exceptions

   Python uses except to catch exceptions, not catch.

2. Step 2: Verify the exception name spelling

   The correct exception name is ZeroDivisionError, not ZeroDivision.

3. Final Answer:

   try: x = 1/0 except ZeroDivisionError: print('Cannot divide by zero') -> Option C

4. Quick Check:

   Use except + exact exception name [OK]

Hint: Use except with exact exception name to catch errors [OK]

Common Mistakes:

• Using 'catch' instead of 'except'
• Misspelling exception names
• Using generic except without specifying error

3. What will be the output of this code?

try:
    num = int('abc')
except ValueError:
    print('Value error caught')
except TypeError:
    print('Type error caught')

medium

A. Value error caught

B. Type error caught

C. No output

D. Program crashes with ValueError

Solution

1. Step 1: Identify the error raised by int('abc')

   Trying to convert 'abc' to int raises a ValueError.

2. Step 2: Match the error with except blocks

   The ValueError is caught by the first except block, so it prints 'Value error caught'.

3. Final Answer:

   Value error caught -> Option A

4. Quick Check:

   int('abc') = ValueError caught [OK]

Hint: Match error type to except block to find output [OK]

Common Mistakes:

• Confusing ValueError with TypeError
• Thinking program crashes without except
• Assuming no output if error caught

4. Find the error in this code and choose the correct fix:

try:
    print(10 / 0)
except ZeroDivisionError, e:
    print('Error:', e)

medium

A. Use except ZeroDivisionError(e):

B. Change except line to: except ZeroDivisionError as e:

C. Change print to print('Error') only

D. Remove the except block completely

Solution

1. Step 1: Identify the syntax error in except clause

   Python 3 requires 'as' to assign exception to a variable, not a comma.

2. Step 2: Correct the except syntax

   Replace except ZeroDivisionError, e: with except ZeroDivisionError as e:.

3. Final Answer:

   Change except line to: except ZeroDivisionError as e: -> Option B

4. Quick Check:

   Use 'as' to assign exception variable [OK]

Hint: Use 'except Exception as e:' syntax in Python 3 [OK]

Common Mistakes:

• Using comma instead of 'as' in except
• Removing except block causing crash
• Wrong parentheses in except clause

5. You want to handle both KeyError and IndexError in the same block. Which is the best way to write the except clause?

hard

A. except KeyError, IndexError:
print('Error caught')

B. except KeyError or IndexError:
print('Error caught')

C. except KeyError and IndexError:
print('Error caught')

D. except (KeyError, IndexError):
print('Error caught')

Solution

1. Step 1: Understand how to catch multiple exceptions

   Python requires a tuple of exceptions inside parentheses to catch multiple exceptions in one block.

2. Step 2: Identify correct tuple syntax

   The correct syntax is except (KeyError, IndexError): to catch both exceptions.

3. Final Answer:

   except (KeyError, IndexError): print('Error caught') -> Option D

4. Quick Check:

   Use tuple in except to catch multiple exceptions [OK]

Hint: Use except (Error1, Error2): to catch multiple exceptions [OK]

Common Mistakes:

• Using 'or' or 'and' instead of tuple
• Using comma without parentheses
• Trying to catch exceptions separately without blocks