Error and Exception Handling

Error vs. Exception

In Python, an error is something that prevents the program from running correctly (e.g., syntax errors). An exception, on the other hand, is a runtime error that occurs when the program attempts to do something invalid (e.g., divide by zero).

Try-Except Block

The try-except block is used to catch and handle exceptions. The basic structure of a try-except block in Python is as follows:

python
try:
    # code to be executed
except ExceptionType:
    # code to handle the exception

Here's an example that uses the ZeroDivisionError exception type:

python
def divide_numbers(a, b):
    try:
        result = a / b
        return result
    except ZeroDivisionError:
        print("Cannot divide by zero!")
        return None
print(divide_numbers(10, 2))  # Output: 5.0
print(divide_numbers(10, 0))  # Output: Cannot divide by zero!

In this example, the divide_numbers function attempts to perform a division operation inside the try block. If the denominator is zero (i.e., a ZeroDivisionError occurs), the except block catches the exception and prints an error message before returning None.

Multiple Exception Types

A try-except block can catch multiple exception types by listing them out in separate except blocks, separated by commas:

python
try:
    # code to be executed
except (TypeError, ZeroDivisionError):
    # code to handle the exceptions

Here's an example that catches both TypeError and ZeroDivisionError:

python
def divide_numbers(a, b):
    try:
        result = a / b
        return result
    except (TypeError, ZeroDivisionError):
        print("Invalid input or division by zero!")
        return None
print(divide_numbers(10, 2))  # Output: 5.0
print(divide_numbers(10, 'a'))  # Output: Invalid input or division by zero!
print(divide_numbers(10, 0))  # Output: Invalid input or division by zero!

In this example, if either a TypeError or a ZeroDivisionError occurs during the execution of the try block, the except block catches the exception and prints an error message before returning None.

Finally Block

A finally block is used to execute code regardless of whether an exception occurred in the try-except block. The basic structure of a try-finally block in Python is as follows:

python
try:
    # code to be executed
finally:
    # code to be executed always

Here's an example that uses a finally block:

python
def divide_numbers(a, b):
    try:
        result = a / b
        return result
    except ZeroDivisionError:
        print("Cannot divide by zero!")
        return None
    finally:
        print("Cleanup code executed!")
print(divide_numbers(10, 2))  # Output: Cleanup code executed!
5.0
print(divide_numbers(10, 0))  # Output: Cannot divide by zero! Cleanup code executed!

In this example, the finally block executes regardless of whether a ZeroDivisionError occurs during the execution of the try-except block.

I hope these examples help illustrate the basics of error handling in Python!