Python Exceptions

In Python, an exception is an event that disrupts the normal flow of a program's execution. When a Python script encounters a situation it cannot handle, it raises an exception. This may occur due to various reasons like division by zero, file not found, invalid syntax, etc. Exceptions are Python objects that represent errors.

Handling Exceptions using try-except

Python provides a way to handle exceptions using a try block followed by one or more except blocks. This prevents your program from crashing and allows you to handle errors gracefully.

Examples

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Error: Division by zero is not allowed!")
            

Handling Multiple Exceptions

You can handle multiple exceptions by specifying different except blocks for different types of exceptions. If you want to handle multiple exceptions in a single block, you can use a tuple of exception types.

try:
    value = int("abc")
    result = 10 / value
except ValueError:
    print("Error: Invalid input, please enter a number!")
except ZeroDivisionError:
    print("Error: Division by zero is not allowed!")
            

The else and finally Clauses

Python's try block can have an optional else block and a finally block:

• The else block is executed if no exceptions are raised in the try block.
• The finally block is always executed, whether an exception occurs or not. It is typically used for cleanup actions.

try:
    num = int(input("Enter a number: "))
    print("You entered:", num)
except ValueError:
    print("Error: Invalid number!")
else:
    print("No exceptions were raised.")
finally:
    print("Execution complete.")
            

Raising Exceptions

You can raise exceptions in your code using the raise keyword. This is useful when you want to enforce certain conditions in your program.

def check_age(age):
    if age < 0:
        raise ValueError("Age cannot be negative!")
    return age

try:
    print(check_age(-5))
except ValueError as e:
    print("Error:", e)
            

Creating Custom Exceptions

Python allows you to create your own exceptions by extending the Exception class. This is useful for creating meaningful error messages specific to your application.

class NegativeNumberError(Exception):
    pass

def check_positive(number):
    if number < 0:
        raise NegativeNumberError("Negative numbers are not allowed!")
    return number

try:
    print(check_positive(-10))
except NegativeNumberError as e:
    print("Error:", e)
            

Exception handling is a crucial aspect of Python programming, enabling you to manage errors gracefully without crashing your programs. By using try, except, else, and finally blocks, you can handle exceptions effectively. Additionally, creating custom exceptions can help you enforce specific conditions and provide meaningful error messages.