Python Error Handling — Exceptions Done Right

Basic Exception Handling

try:
    result = 10 / 0
except ZeroDivisionError as e:
    print(f'Error: {e}')
except (TypeError, ValueError) as e:
    print(f'Type or value error: {e}')
except Exception as e:
    print(f'Unexpected error: {e}')
else:
    print('No error occurred')
finally:
    print('Always runs')

Custom Exceptions

class InsufficientFundsError(Exception):
    def __init__(self, balance, amount):
        self.balance = balance
        self.amount = amount
        super().__init__(f'Cannot withdraw ${amount}. Balance: ${balance}')

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

try:
    withdraw(100, 150)
except InsufficientFundsError as e:
    print(e)  # Cannot withdraw $150. Balance: $100

Raising Exceptions

def set_age(age):
    if not isinstance(age, int):
        raise TypeError('Age must be an integer')
    if age < 0 or age > 150:
        raise ValueError(f'Age must be between 0 and 150, got {age}')
    return age