How do you create and raise custom exceptions in Python? Python में custom exceptions कैसे बनाएं और raise करें?

Custom exceptions are created by subclassing Exception (or a more specific built-in exception), allowing you to represent domain-specific error conditions clearly.

class InsufficientFundsError(Exception):
    """Raised when a withdrawal exceeds the account balance."""
    def __init__(self, balance, amount):
        self.balance = balance
        self.amount = amount
        message = f'Cannot withdraw {amount}, balance is only {balance}'
        super().__init__(message)

class BankAccount:
    def __init__(self, balance):
        self.balance = balance

    def withdraw(self, amount):
        if amount > self.balance:
            raise InsufficientFundsError(self.balance, amount)
        self.balance -= amount
        return self.balance

account = BankAccount(100)
try:
    account.withdraw(150)
except InsufficientFundsError as e:
    print(e)  # Cannot withdraw 150, balance is only 100
    print(e.balance, e.amount)  # access custom attributes

# Building an exception hierarchy for a project
class AppError(Exception):
    """Base exception for the application."""
    pass

class ValidationError(AppError):
    pass

class NotFoundError(AppError):
    pass

# Callers can catch the base class to handle ANY app-specific error
try:
    raise ValidationError('Invalid email format')
except AppError as e:
    print(f'App error: {e}')