Try–except execution flow in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of try-except with no error

What is the output of this code when no error occurs?

Python

try:
    print("Start")
    result = 10 / 2
    print("Result is", result)
except ZeroDivisionError:
    print("Division by zero!")
finally:
    print("End")

A Division by zero!\nEnd

B Start\nDivision by zero!\nEnd

C Start\nEnd

D Start\nResult is 5.0\nEnd

💡 Hint

Remember that except block runs only if an error occurs.

Since 10 divided by 2 is valid, no exception occurs. So the try block runs fully, printing 'Start' and 'Result is 5.0'. The finally block always runs, printing 'End'.

❓ Predict Output

intermediate

Output when exception occurs and is caught

What is the output of this code when a ZeroDivisionError occurs?

Python

try:
    print("Start")
    result = 10 / 0
    print("Result is", result)
except ZeroDivisionError:
    print("Division by zero!")
finally:
    print("End")

A Start\nDivision by zero!\nEnd

B Start\nResult is 0\nEnd

C Division by zero!\nEnd

D Start\nEnd

💡 Hint

Division by zero causes an exception, so except block runs.

The division by zero raises ZeroDivisionError, so the except block prints 'Division by zero!'. The finally block always runs, printing 'End'.

❓ Predict Output

advanced

Output with multiple except blocks

What is the output of this code?

Python

try:
    print("Start")
    x = int('abc')
    print("Parsed", x)
except ValueError:
    print("Value error caught")
except ZeroDivisionError:
    print("Zero division error caught")
finally:
    print("End")

A Start\nEnd

B Start\nValue error caught\nEnd

C Start\nParsed abc\nEnd

D Start\nZero division error caught\nEnd

💡 Hint

int('abc') raises ValueError.

Trying to convert 'abc' to int raises ValueError, so the first except block runs. The finally block always runs.

❓ Predict Output

advanced

Output when exception not caught

What happens when an exception is raised but not caught by except blocks?

Python

try:
    print("Start")
    x = [1, 2, 3]
    print(x[5])
except ZeroDivisionError:
    print("Zero division error caught")
finally:
    print("End")

A Start\nEnd\nIndexError exception raised

B Start\nZero division error caught\nEnd

C Start\nEnd

D IndexError exception raised

💡 Hint

IndexError is not caught by ZeroDivisionError except block.

Accessing x[5] raises IndexError, which is not caught. The finally block runs printing 'End'. Then the program raises IndexError.

🧠 Conceptual

expert

Order of execution in try-except-finally

Which option correctly describes the order of execution when an exception occurs inside the try block and is caught?

A finally block runs first, then try block, then except block

B except block runs first, then try block, then finally block

C try block runs until exception, except block runs, finally block runs

D try block runs fully, finally block runs, except block runs

💡 Hint

Think about what happens when an error occurs inside try.

When an exception occurs, the try block stops at the error, the except block runs to handle it, then the finally block runs always.

Practice

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

easy

A. To speed up the program execution

B. To handle errors and prevent the program from crashing

C. To repeat a block of code multiple times

D. To define a new function

Solution

1. Step 1: Understand the role of try block

   The try block contains code that might cause an error during execution.

2. Step 2: Understand the role of except block

   The except block catches and handles the error so the program does not stop abruptly.

3. Final Answer:

   To handle errors and prevent the program from crashing -> Option B

4. Quick Check:

   Try-except handles errors = B [OK]

Hint: Try-except blocks catch errors to keep programs running [OK]

Common Mistakes:

• Thinking try-except speeds up code
• Confusing try-except with loops
• Using try-except to define functions

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

easy

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

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

C. try:
x = 1/0
except:
print('Error')
finally ZeroDivisionError:

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

Solution

1. Step 1: Identify correct try-except syntax

   Python uses try: followed by except ExceptionType: to catch errors.

2. Step 2: Check each option for syntax errors

   try: x = 1/0 except ZeroDivisionError: print('Cannot divide by zero') uses correct except ZeroDivisionError: syntax; others use invalid keywords like catch or incorrect formatting.

3. Final Answer:

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

4. Quick Check:

   Correct except syntax = A [OK]

Hint: Use 'except ExceptionType:' to catch specific errors [OK]

Common Mistakes:

• Using 'catch' instead of 'except'
• Adding 'then' after except
• Misplacing 'finally' keyword

3. What will be the output of the following code?

try:
    print('Start')
    x = 5 / 0
    print('End')
except ZeroDivisionError:
    print('Error caught')
print('Done')

medium

A. Start
End
Error caught
Done

B. Error caught
Done

C. Start
Done

D. Start
Error caught
Done

Solution

1. Step 1: Trace code inside try block

   It prints 'Start', then tries to divide 5 by 0, which raises ZeroDivisionError before printing 'End'.

2. Step 2: Handle exception and continue

   The except block catches the error and prints 'Error caught'. After that, the program continues and prints 'Done'.

3. Final Answer:

   Start Error caught Done -> Option D

4. Quick Check:

   Exception stops try block, except runs = C [OK]

Hint: Error stops try; except runs; code after try-except runs [OK]

Common Mistakes:

• Assuming 'End' prints after error
• Missing that except block runs
• Thinking program stops after error

4. Identify the error in this code snippet:

try:
    print('Hello')
except ValueError
    print('Value error occurred')

medium

A. try block cannot have print statements

B. Missing parentheses after except

C. Missing colon ':' after except ValueError

D. except block must come before try block

Solution

1. Step 1: Check syntax of except statement

   The except line must end with a colon ':' to define the block.

2. Step 2: Identify missing colon

   In the code, except ValueError is missing the colon, causing a syntax error.

3. Final Answer:

   Missing colon ':' after except ValueError -> Option C

4. Quick Check:

   except line needs ':' = A [OK]

Hint: Always put ':' after except ExceptionType [OK]

Common Mistakes:

• Forgetting colon after except
• Adding parentheses after except
• Misordering try and except blocks

5. You want to safely convert user input to an integer, using try-except-else and catching ValueError specifically, printing 'Invalid input' for invalid input and 'Input is', num for valid input, without stopping the program. Which code does this?

hard

A. try:
num = int(input('Enter number: '))
except ValueError:
print('Invalid input')
else:
print('Input is', num)

B. try:
num = int(input('Enter number: '))
except:
print('Invalid input')
else:
print('Input is', num)

C. try:
num = int(input('Enter number: '))
except ValueError:
print('Invalid input')
finally:
print('Done')

D. try:
num = int(input('Enter number: '))
except ValueError:
print('Invalid input')

Solution

1. Step 1: Understand try-except-else structure

   The try block attempts conversion; except handles errors; else runs if no error occurs.

2. Step 2: Check which option prints 'Invalid input' on error and shows input if valid

   try: num = int(input('Enter number: ')) except ValueError: print('Invalid input') else: print('Input is', num) correctly prints 'Invalid input' on ValueError and prints the number if conversion succeeds.

3. Final Answer:

   try: num = int(input('Enter number: ')) except ValueError: print('Invalid input') else: print('Input is', num) -> Option A

4. Quick Check:

   Use except for errors, else for success = D [OK]

Hint: Use except for errors and else for success actions [OK]

Common Mistakes:

• Not using else to handle successful input
• Catching all exceptions without specifying
• Missing error handling causing crash