Python Custom Exceptions Interview Questions

Q1. How do you create a custom exception in Python?

Define a new class that inherits from Exception (or a subclass).
Example:

class NegativeNumberError(Exception):
    pass

You can add custom attributes and __init__ for more information.

Q2. Why would you use custom exceptions?

Custom exceptions make your code more readable and allow you to handle specific error conditions in a domain-specific way.
They can carry additional context (like an error code) and can be caught separately from built-in exceptions.

Q3. How do you raise a custom exception?

Just like any exception, use raise.
Example:

if value < 0:
    raise NegativeNumberError("Value cannot be negative")

Q4. Can custom exceptions have additional attributes?

Yes, you can define __init__ to set custom attributes.
Example:

class ValidationError(Exception):
    def __init__(self, field, message):
        self.field = field
        self.message = message
        super().__init__(f"{field}: {message}")

Q5. How do you catch a custom exception?

Same as built-in exceptions.
Example:

try:
    # code that might raise NegativeNumberError
except NegativeNumberError as e:
    print(f"Error: {e}")

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