Creating exception classes in Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a new exception class named MyError that inherits from Exception.

Python

class MyError([1]):
    pass

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

ABaseException

BException

CError

Dobject

Attempts:

3 left

💡 Hint

Common Mistakes

Inheriting from 'object' instead of 'Exception'.

Using 'Error' which is not a built-in base class.

To create a custom exception, you inherit from the built-in Exception class.

2fill in blank

medium

Complete the code to raise the custom exception MyError with the message 'Oops!'.

Python

raise [1]('Oops!')

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

AMyError

BException

CError

DBaseException

Attempts:

3 left

💡 Hint

Common Mistakes

Raising the base Exception instead of the custom one.

Using a class name that was not defined.

You raise your custom exception class by calling it with a message.

3fill in blank

hard

Fix the error in the code to correctly define a custom exception MyError that inherits from Exception.

Python

class MyError(Exception):
    def __init__(self, message):
        super().[1](message)

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

A__init__

Binit

Cconstructor

Dsuper_init

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'init' without underscores.

Using a made-up method name like 'constructor'.

The correct method name to call the parent constructor is __init__.

4fill in blank

hard

Fill both blanks to define a custom exception MyError that stores a message and returns it when converted to string.

Python

class MyError(Exception):
    def __init__(self, [1]):
        self.[2] = [1]

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

Amessage

Bmsg

Cerror

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for parameter and attribute causing errors.

Using undefined variable names.

The parameter and the attribute should have the same name to store the message.

5fill in blank

hard

Fill both blanks to complete the __str__ method that returns the error message of MyError.

Python

class MyError(Exception):
    def __init__(self, message):
        self.message = message
    def __str__(self):
        return [1].[2]

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

Aself

Bmessage

Cmsg

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Returning undefined variables.

Not using 'self' to access attributes.

The __str__ method returns self.message to show the error message.

Practice

1. What is the correct way to create a custom exception class in Python?

easy

A. exception MyError(Exception): pass

B. def MyError(): raise Exception

C. class MyError(Exception): pass

D. class MyError: pass

Solution

1. Step 1: Understand how to define a class inheriting Exception

   Custom exceptions must inherit from the built-in Exception class to behave like errors.

2. Step 2: Check syntax correctness

   class MyError(Exception): pass correctly defines a class named MyError inheriting from Exception with pass inside.

3. Final Answer:

   class MyError(Exception): pass -> Option C

4. Quick Check:

   Custom exception class = class MyError(Exception): pass [OK]

Hint: Inherit from Exception to create custom errors [OK]

Common Mistakes:

• Not inheriting from Exception
• Using def instead of class
• Wrong keyword like 'exception' instead of 'class'

2. Which of the following is the correct syntax to raise a custom exception named MyError?

easy

A. raise MyError()

B. throw MyError()

C. raise new MyError()

D. throw new MyError()

Solution

1. Step 1: Recall the Python keyword to raise exceptions

   Python uses the keyword 'raise' to trigger exceptions, not 'throw'.

2. Step 2: Check the syntax for raising a custom exception

   Correct syntax is 'raise MyError()' to create and raise the exception instance.

3. Final Answer:

   raise MyError() -> Option A

4. Quick Check:

   Raise custom error = raise MyError() [OK]

Hint: Use 'raise' keyword followed by exception instance [OK]

Common Mistakes:

• Using 'throw' instead of 'raise'
• Adding 'new' keyword like in other languages
• Not calling the exception as a function

3. What will be the output of this code?

class MyError(Exception):
    pass

try:
    raise MyError("Oops!")
except MyError as e:
    print(e)

medium

A. Oops!

B. MyError

C. Exception

D. No output

Solution

1. Step 1: Understand the raise statement with message

   The code raises MyError with the message 'Oops!'.

2. Step 2: Catch the exception and print its message

   The except block catches MyError as 'e' and prints 'e', which outputs the message 'Oops!'.

3. Final Answer:

   Oops! -> Option A

4. Quick Check:

   Exception message prints = Oops! [OK]

Hint: Exception instance prints its message string [OK]

Common Mistakes:

• Printing exception class name instead of message
• Not catching the exception properly
• Expecting no output

4. Identify the error in this code snippet:

class MyError(Exception):
    pass

try:
    raise MyError
except MyError:
    print("Caught error")

medium

A. Incorrect exception name in except block

B. No error, code runs fine

C. Syntax error in class definition

D. Missing parentheses when raising MyError

Solution

1. Step 1: Check how the exception is raised

   In Python, it is valid to raise an exception class without parentheses if it has no __init__ arguments.

2. Step 2: Identify the problem in the code

   The code uses 'raise MyError' without parentheses, which is valid and does not raise an error.

3. Final Answer:

   No error, code runs fine -> Option B

4. Quick Check:

   Raising exception class without parentheses is allowed [OK]

Hint: Raising exception class without parentheses is valid if no arguments [OK]

Common Mistakes:

• Omitting parentheses after exception name
• Mismatching exception names in except block
• Incorrect class syntax

5. You want to create a custom exception ValidationError that stores an error code along with the message. Which code correctly implements this?

hard

A. class ValidationError(Exception):
def __init__(self, message):
self.code = 0
super().__init__(message)

B. class ValidationError(Exception):
def __init__(self, message, code):
self.message = message
self.code = code

C. class ValidationError(Exception):
def __init__(self, code):
super().__init__(code)

D. class ValidationError(Exception):
def __init__(self, message, code):
super().__init__(message)
self.code = code

Solution

1. Step 1: Understand how to extend Exception with extra attributes

   To add an error code, override __init__ and call super().__init__(message) to set the message properly.

2. Step 2: Check which option correctly calls super().__init__ and stores code

   class ValidationError(Exception): def __init__(self, message, code): super().__init__(message) self.code = code calls super().__init__(message) and assigns self.code = code, correctly storing both.

3. Final Answer:

   class ValidationError(Exception): def __init__(self, message, code): super().__init__(message) self.code = code -> Option D

4. Quick Check:

   Call super().__init__(message) and store extra attributes [OK]

Hint: Call super().__init__(message) to set message, then add code [OK]

Common Mistakes:

• Not calling super().__init__ for message
• Assigning message without super call
• Missing code attribute assignment