Custom error messages in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to raise a ValueError with a custom message.

Python

if age < 0:
    raise ValueError([1])

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

A"Age cannot be negative"

BAge cannot be negative

CValueError

Dprint("Error")

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the message

Using a variable name instead of a string

Trying to print instead of raise

The raise statement needs a string message inside quotes to show a custom error message.

2fill in blank

medium

Complete the code to raise a TypeError with a custom message when input is not a string.

Python

if not isinstance(name, str):
    raise TypeError([1])

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

AInput must be a string

BTypeError

C"Input must be a string"

Dprint("Wrong type")

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes for the message

Raising the wrong error type

Using print instead of raise

The error message must be a string inside quotes to explain the type error.

3fill in blank

hard

Fix the error in raising a custom error message for zero division.

Python

if denominator == 0:
    raise ZeroDivisionError([1])

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

Aprint("Error")

BZeroDivisionError

C0

D"Cannot divide by zero"

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the error class instead of a message

Using print instead of raise

Passing a number instead of a string

The message must be a string explaining the error, inside quotes.

4fill in blank

hard

Fill both blanks to raise a custom error with a message including the invalid value.

Python

if score < 0 or score > 100:
    raise ValueError(f"Invalid score: [1]")

# Use the variable name in the message
invalid_value = [2]

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

Ascore

Bvalue

Dscore_value

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong variable name

Not using the variable inside the f-string

Assigning invalid_value to a non-existent variable

The variable 'score' holds the invalid value and should be used in the message and assigned to invalid_value.

5fill in blank

hard

Fill all three blanks to raise a custom error with a message showing the invalid input and its type.

Python

if not isinstance(data, dict):
    raise TypeError(f"Expected dict but got [1] of type [2]")

actual_type = type([3]).__name__

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

Adata

Dinput

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in blanks

Not using f-string formatting

Forgetting to get the type name with __name__

The variable 'data' is used to show the invalid input and get its type name.

Practice

1. What is the main purpose of using raise ValueError('Custom message') in Python?

easy

A. To print a warning message without stopping the program.

B. To stop the program and show a specific error message when a condition is not met.

C. To automatically fix errors in the code.

D. To ignore errors and continue running the program.

Solution

1. Step 1: Understand the raise statement

   The raise keyword is used to stop the program and throw an error.

2. Step 2: Purpose of custom messages

   Adding a message like 'Custom message' helps explain why the error happened.

3. Final Answer:

   To stop the program and show a specific error message when a condition is not met. -> Option B

4. Quick Check:

   raise with message = stop and explain error [OK]

Hint: Raise errors to stop and explain problems clearly [OK]

Common Mistakes:

• Thinking raise only prints messages without stopping
• Confusing raise with print or logging
• Believing raise fixes errors automatically

2. Which of the following is the correct syntax to raise a custom error with message "Invalid input"?

easy

A. raise 'Invalid input' ValueError

B. throw ValueError('Invalid input')

C. error ValueError('Invalid input')

D. raise ValueError('Invalid input')

Solution

1. Step 1: Identify the correct keyword

   In Python, raise is used to throw errors, not throw or error.

2. Step 2: Correct order of error and message

   The syntax is raise ErrorType('message'), so the error type comes first, then the message in parentheses.

3. Final Answer:

   raise ValueError('Invalid input') -> Option D

4. Quick Check:

   raise + ErrorType('message') = correct syntax [OK]

Hint: Use raise ErrorType('message') to create custom errors [OK]

Common Mistakes:

• Using throw instead of raise
• Placing message before error type
• Missing parentheses around the message

3. What will be the output of this code?

def check_age(age):
    if age < 18:
        raise ValueError('Age must be 18 or older')
    return 'Access granted'

print(check_age(16))

medium

A. Access granted

B. None

C. ValueError: Age must be 18 or older

D. SyntaxError

Solution

1. Step 1: Check the condition in the function

   The function raises a ValueError if age is less than 18. Here, age is 16, so the error triggers.

2. Step 2: Understand what happens on raise

   When the error is raised, the program stops and shows the error message instead of returning 'Access granted'.

3. Final Answer:

   ValueError: Age must be 18 or older -> Option C

4. Quick Check:

   raise triggers error output = ValueError message [OK]

Hint: If condition fails, raise stops and shows error message [OK]

Common Mistakes:

• Expecting function to return 'Access granted' anyway
• Confusing error message with print output
• Thinking raise prints message but continues

4. Find the error in this code snippet:

def check_number(num):
    if num < 0:
        raise 'Negative number error'
    return 'Number is positive'

print(check_number(-5))

medium

A. You cannot raise a string directly; it must be an Exception type.

B. The raise statement is missing parentheses.

C. The function should return None instead of a string.

D. The if condition should be num > 0.

Solution

1. Step 1: Check the raise statement

   The code tries to raise a string directly, which is not allowed in Python. Only Exception types can be raised.

2. Step 2: Correct way to raise errors

   Use raise ValueError('message') or another Exception class, not a plain string.

3. Final Answer:

   You cannot raise a string directly; it must be an Exception type. -> Option A

4. Quick Check:

   raise must use Exception type, not string [OK]

Hint: Always raise Exception objects, not strings [OK]

Common Mistakes:

• Raising strings instead of Exception classes
• Forgetting to include parentheses with message
• Changing condition incorrectly

5. You want to create a function validate_score(score) that raises a ValueError with the message "Score must be between 0 and 100" if the score is outside this range. Which code correctly implements this?

hard

A. def validate_score(score):
if score < 0 or score > 100:
raise ValueError('Score must be between 0 and 100')
return 'Valid score'

B. def validate_score(score):
if 0 <= score <= 100:
raise ValueError('Score must be between 0 and 100')
return 'Valid score'

C. def validate_score(score):
if score < 0 and score > 100:
raise ValueError('Score must be between 0 and 100')
return 'Valid score'

D. def validate_score(score):
if score == 0 or score == 100:
raise ValueError('Score must be between 0 and 100')
return 'Valid score'

Solution

1. Step 1: Understand the valid range condition

   The score is valid if it is between 0 and 100 inclusive. So invalid means less than 0 or greater than 100.

2. Step 2: Check the if condition logic

   def validate_score(score): if score < 0 or score > 100: raise ValueError('Score must be between 0 and 100') return 'Valid score' correctly uses if score < 0 or score > 100 to detect invalid scores and raise the error.

3. Final Answer:

   def validate_score(score): if score < 0 or score > 100: raise ValueError('Score must be between 0 and 100') return 'Valid score' -> Option A

4. Quick Check:

   Use or for invalid range, raise error if outside [OK]

Hint: Raise error if score is less than 0 or greater than 100 [OK]

Common Mistakes:

• Using and instead of or in condition
• Raising error for valid scores instead of invalid
• Checking only equality instead of range