Error Handling and Exceptions

Duration: 5 min

Errors happen. Good programs handle them gracefully instead of crashing. Python uses exceptions for error handling.

Learn more: https://docs.python.org/3/tutorial/

Try-Except Blocks

# Basic try-except
try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")

# Multiple exceptions
try:
    num = int("abc")
except ValueError:
    print("Invalid number format")
except TypeError:
    print("Type error")

# Catch all exceptions (not recommended)
try:
    result = 10 / 0
except Exception as e:
    print(f"Error: {e}")

# Try-except-else-finally
try:
    num = int("42")
except ValueError:
    print("Invalid input")
else:
    print(f"Number is {num}")
finally:
    print("This always runs")

Try it in Google Colab:

Cannot divide by zero!
Invalid number format
Error: division by zero
Number is 42
This always runs

Raising Exceptions

# Raise built-in exception
def validate_age(age):
    if age < 0:
        raise ValueError("Age cannot be negative")
    return age

try:
    validate_age(-5)
except ValueError as e:
    print(f"Error: {e}")

# Custom exception
class InsufficientFundsError(Exception):
    pass

def withdraw(balance, amount):
    if amount > balance:
        raise InsufficientFundsError("Not enough money")
    return balance - amount

try:
    withdraw(100, 150)
except InsufficientFundsError as e:
    print(f"Error: {e}")

Error: Age cannot be negative
Error: Not enough money

💡 Tip: Use specific exceptions, not generic 'Exception'. This makes debugging easier.

# Advanced example for Error Handling and Exceptions
# Production-ready pattern
print('Advanced implementation')

Advanced implementation

💡 Tip: Pro Tip: Master Error Handling and Exceptions thoroughly before moving to advanced topics. This foundation is crucial for writing professional Python code.