Try–except–finally behavior in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to catch a ZeroDivisionError.

Python

try:
    result = 10 / 0
except [1]:
    print("Cannot divide by zero")

Drag options to blanks, or click blank then click option'

AZeroDivisionError

BValueError

CTypeError

DIndexError

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong exception type like ValueError or TypeError.

Not catching any exception and letting the program crash.

The ZeroDivisionError is raised when dividing by zero. Catching it allows the program to handle this error gracefully.

2fill in blank

medium

Complete the code to always print 'Done' after the try-except block.

Python

try:
    x = int('abc')
except ValueError:
    print('Invalid number')
finally:
    [1]('Done')

Drag options to blanks, or click blank then click option'

Ainput

Breturn

Cprint

Draise

Attempts:

3 left

💡 Hint

Common Mistakes

Using input instead of print.

Trying to raise an exception inside finally without reason.

The finally block runs no matter what. Using print here outputs 'Done' always.

3fill in blank

hard

Fix the error in the except clause to catch the correct exception.

Python

try:
    numbers = [1, 2, 3]
    print(numbers[5])
except [1]:
    print('Index out of range')

Drag options to blanks, or click blank then click option'

AKeyError

BTypeError

CValueError

DIndexError

Attempts:

3 left

💡 Hint

Common Mistakes

Using KeyError which is for dictionaries.

Using ValueError which is for wrong values.

Accessing an invalid list index raises IndexError. Catching this exception handles the error properly.

4fill in blank

hard

Fill both blanks to catch a ValueError and print a message, then always print 'Finished'.

Python

try:
    num = int('abc')
except [1]:
    print('Conversion failed')
finally:
    [2]('Finished')

Drag options to blanks, or click blank then click option'

AValueError

Bprint

CZeroDivisionError

Dinput

Attempts:

3 left

💡 Hint

Common Mistakes

Catching the wrong exception type.

Using input instead of print in finally.

The except block catches ValueError from invalid int conversion. The finally block prints 'Finished' always.

5fill in blank

hard

Fill all three blanks to catch a KeyError, print the error message, and always print 'End'.

Python

my_dict = {'a': 1}
try:
    value = my_dict[[1]]
except [2] as e:
    [3](f'Error: {e}')
finally:
    print('End')

Drag options to blanks, or click blank then click option'

A'b'

BKeyError

Cprint

D'a'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a key that exists, so no error occurs.

Catching the wrong exception type.

Not printing the error message correctly.

Accessing key 'b' causes a KeyError. Catching it as e allows printing the error message. The finally block prints 'End' always.

Practice

1. What does the finally block do in a try-except-finally structure?

easy

A. It always runs, whether an error occurs or not.

B. It runs only if an error occurs.

C. It runs only if no error occurs.

D. It runs before the try block.

Solution

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

   The try block runs code that might cause an error, and except runs only if an error happens.

2. Step 2: Understand the finally block behavior

   The finally block always runs after try and except, no matter if an error occurred or not.

3. Final Answer:

   It always runs, whether an error occurs or not. -> Option A

4. Quick Check:

   finally always runs = A [OK]

Hint: Remember: finally always runs last, no matter what. [OK]

Common Mistakes:

• Thinking finally runs only on errors
• Confusing except and finally blocks
• Believing finally runs before try

2. Which of the following is the correct syntax for a try-except-finally block in Python?

easy

A. except:
pass
try:
pass
finally:
pass

B. try:
pass
finally:
pass
except:
pass

C. try:
pass
except:
pass
finally:
pass

D. try:
pass
except:
pass
else:
pass

Solution

1. Step 1: Recall the order of blocks

   The correct order is try, then except, then finally.

2. Step 2: Check each option's order

   try: pass except: pass finally: pass follows the correct order. try: pass finally: pass except: pass places finally before except, which is invalid. except: pass try: pass finally: pass starts with except, which is wrong. try: pass except: pass else: pass uses else but no finally.

3. Final Answer:

   try, except, finally in correct order -> Option C

4. Quick Check:

   try-except-finally order = C [OK]

Hint: Remember order: try, except, then finally. [OK]

Common Mistakes:

• Placing finally before except
• Starting with except block
• Confusing else with finally

3. What will be the output of this code?

try:
    print('Start')
    x = 1 / 0
except ZeroDivisionError:
    print('Error caught')
finally:
    print('Always runs')

medium

A. Start\nAlways runs

B. Start\nError caught

C. Error caught\nAlways runs

D. Start\nError caught\nAlways runs

Solution

1. Step 1: Trace the try block

   The code prints 'Start' then tries to divide by zero, causing a ZeroDivisionError.

2. Step 2: Handle the exception and finally block

   The except block catches the error and prints 'Error caught'. Then the finally block runs and prints 'Always runs'.

3. Final Answer:

   Start\nError caught\nAlways runs -> Option D

4. Quick Check:

   try prints + except prints + finally prints = A [OK]

Hint: finally always prints last, even after except. [OK]

Common Mistakes:

• Forgetting finally runs
• Assuming code stops after error
• Missing the initial print before error

4. Find the error in this code snippet:

try:
    print('Hello')
except:
    print('Error')
finally
    print('Done')

medium

A. Missing colon after except

B. Missing colon after finally

C. Indentation error in try block

D. No error, code is correct

Solution

1. Step 1: Check syntax of try-except-finally

   Each block header must end with a colon (:). The finally line is missing a colon.

2. Step 2: Verify other parts

   The except line has a colon, and indentation is correct.

3. Final Answer:

   Missing colon after finally -> Option B

4. Quick Check:

   Colon needed after finally = B [OK]

Hint: Check colons after try, except, finally lines. [OK]

Common Mistakes:

• Ignoring missing colon errors
• Confusing except and finally syntax
• Assuming indentation fixes missing colon

5. Consider this code:

def test():
    try:
        return 'try'
    except:
        return 'except'
    finally:
        return 'finally'

result = test()
print(result)

What will be printed?

hard

A. finally

B. except

C. None

D. try

Solution

1. Step 1: Understand return in try and finally

   The try block returns 'try', but the finally block also has a return statement.

2. Step 2: Know that finally return overrides others

   In Python, if finally has a return, it overrides any previous return from try or except.

3. Step 3: Determine final output

   The function returns 'finally', so print(result) outputs 'finally'.

4. Final Answer:

   finally -> Option A

5. Quick Check:

   finally return overrides try/except returns = D [OK]

Hint: Return in finally overrides try/except returns. [OK]

Common Mistakes:

• Thinking try return is final
• Ignoring finally's return effect
• Assuming except runs without error