try / except

try / except

In this tutorial, we'll catch expected errors and keep a program running.

Use try / except to handle an exception without crashing the program.

try:
    age = int(input("Age: "))
    print("Next birthday:", age + 1)
except ValueError:
    print("Please enter a whole number")

If the conversion works, Python skips the except block. If int() raises ValueError, Python runs the except block.

The Shape

try:
    risky_code
except SomeError:
    code_to_run_if_that_error_happens

Put only the risky code inside try. If the block is huge, it becomes harder to know which line caused the problem.

Example: Safe Division

try:
    total = 10 / 0
    print(total)
except ZeroDivisionError:
    print("Cannot divide by zero")

The program handles the error and continues.

Handling User Input

text = input("Enter a number: ")

try:
    number = int(text)
    print(number * 2)
except ValueError:
    print("That was not a valid number")

This is a common beginner use case.

Common Mistake

Do not use a bare except while learning:

try:
    number = int("hello")
except:
    print("Something went wrong")

This catches every error, even ones you did not expect. Specific exceptions are clearer.

Practice

Ask the user for a number. If they enter valid input, print the number doubled. If not, print a helpful message.