11. Error Handling with try/except

Why Handle Errors?

Errors happen—network issues, wrong user input, missing files. Without error handling, your program will crash. With try/except, you can catch errors and respond gracefully instead of crashing.

Basic try/except

try:
    number = int(input("Enter a number: "))
    print(10 / number)
except:
    print("Something went wrong!")

Catching Specific Errors

Python errors have names like ValueError, FileNotFoundError, ZeroDivisionError, etc. You can handle them individually.

try:
    number = int(input("Enter a number: "))
    print(10 / number)
except ValueError:
    print("Please enter a valid number.")
except ZeroDivisionError:
    print("You can't divide by zero!")

Using else and finally

`else` runs only if no error occurs. `finally` runs no matter what—perfect for cleanup actions.

try:
    result = 10 / 2
except ZeroDivisionError:
    print("Math error")
else:
    print("Success! Result is", result)
finally:
    print("This always runs.")

Raising Your Own Errors

Use `raise` to trigger errors intentionally when something is wrong.

def withdraw(amount):
    if amount <= 0:
        raise ValueError("Amount must be greater than zero")
    print(f"Withdrew ${amount}")

withdraw(-50)

Common Exception Types

All Built-in Python Exceptions

Mini Project Step

Add error handling to your calculator program. Catch invalid numbers and division by zero using try/except, and show a friendly message instead of crashing.