Error Handling in Python

1. The try/except Block

The try and except keywords help us catch and handle errors in Python. By putting code that might cause an error inside a try block, we can catch specific errors in the except block.

Example

In this example, we are dividing two numbers. If the second number is zero, it will cause an error. By using try and except, we can handle this error:

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

Explanation: If dividing by zero causes an error, Python will skip the rest of the try block and run the except block, printing Cannot divide by zero!

2. Catching Different Errors

We can handle multiple errors by using different except blocks for each error type.

Example

try:
    my_list = [1, 2, 3]
    print(my_list[5]) # IndexError
except IndexError:
    print("Index is out of range!")
except ZeroDivisionError:
    print("Cannot divide by zero!")

Explanation: Here, we handle both IndexError and ZeroDivisionError. If we try to access an index that doesn't exist, it will print Index is out of range!

3. The else and finally Blocks

The else block runs only if no errors occur, while finally runs no matter what.

Example

try:
    result = 10 / 2
except ZeroDivisionError:
    print("Cannot divide by zero!")
else:
    print("Division successful:", result)
finally:
    print("This will always run.")

Explanation: else runs if there is no error. finally runs whether or not an error occurred, often used for cleanup tasks.

4. Using Assertions

assert is used to test conditions and stop the program if the condition is False. It is helpful for debugging by ensuring assumptions are correct.

Example

def get_positive_number(num):
    assert num > 0, "Number must be positive"
    return num

print(get_positive_number(5))   # Works fine
print(get_positive_number(-2))  # Raises AssertionError

Explanation: If num is not positive, assert will raise an AssertionError with the message "Number must be positive".