Extending built-in exceptions in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of custom exception with additional attribute

What is the output of this code when the exception is caught and printed?

Python

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

try:
    raise MyError("Oops!", 404)
except MyError as e:
    print(f"Error: {e}, Code: {e.code}")

A Error: Oops!, Code: e.code

B Error: MyError('Oops!'), Code: 404

C Error: Oops!, Code: None

D Error: Oops!, Code: 404

💡 Hint

Look at how the message and code are passed and accessed in the exception.

The custom exception stores the message in the base Exception class and the code in a new attribute. Printing the exception object shows the message, and accessing e.code gives 404.

❓ Predict Output

intermediate

Output of overridden __str__ in custom exception

What will be printed when this code runs?

Python

class CustomError(Exception):
    def __init__(self, message, severity):
        super().__init__(message)
        self.severity = severity
    def __str__(self):
        return f"{self.args[0]} (Severity: {self.severity})"

try:
    raise CustomError("Failed operation", "High")
except CustomError as e:
    print(e)

A Failed operation (Severity: severity)

B Failed operation (Severity: High)

C Failed operation

D CustomError('Failed operation', 'High')

💡 Hint

The __str__ method controls how the exception is printed.

The __str__ method returns a formatted string combining the message and severity, so printing the exception shows that string.

🔧 Debug

advanced

Identify the error in custom exception initialization

This code tries to create a custom exception but raises an error. What is the cause?

Python

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

try:
    raise BadError("Error happened", 500)
except BadError as e:
    print(e)

A AttributeError because 'code' is missing

B SyntaxError due to missing colon

C TypeError because Exception __init__ is not called

D No error, prints 'Error happened'

💡 Hint

Check if the base Exception class is properly initialized.

The custom exception does not call super().__init__(message), so the base Exception is not initialized, causing a TypeError when printing.

📝 Syntax

advanced

Syntax error in custom exception definition

Which option contains a syntax error in defining a custom exception?

A

class MyException(Exception)
    def __init__(self, msg):
        super().__init__(msg)

B

class MyException(Exception):
    def __init__(self, msg):
        super().__init__(msg)
    def __str__(self):
        return self.args[0]

C

class MyException(Exception):
    pass

D

class MyException(Exception):
    def __init__(self, msg):
        super().__init__(msg)

💡 Hint

Check the class definition syntax carefully.

Option A is missing a colon ':' after the class declaration, causing a SyntaxError.

🚀 Application

expert

Determine the output of nested custom exceptions

What is the output of this code snippet?

Python

class BaseError(Exception):
    def __init__(self, message):
        super().__init__(message)

class DerivedError(BaseError):
    def __init__(self, message, code):
        super().__init__(message)
        self.code = code

try:
    try:
        raise DerivedError("Failure", 123)
    except DerivedError as e:
        raise BaseError(f"Wrapped: {e}") from e
except BaseError as e:
    print(e)
    print(type(e.__cause__))

A

Wrapped: Failure
<class '__main__.DerivedError'>

B

Wrapped: Failure
<class '__main__.BaseError'>

C

Failure
<class '__main__.BaseError'>

D

Failure
<class '__main__.DerivedError'>

💡 Hint

Look at how exception chaining with 'from' works and what __cause__ stores.

The outer exception message is 'Wrapped: Failure'. The __cause__ attribute points to the original DerivedError instance, so its type is DerivedError.