Understanding Python Exceptions

Python exceptions are events that occur during the execution of a program that disrupt the normal flow of instructions. They are crucial for error handling in Python, allowing developers to manage issues gracefully.

Key Concepts

• What are Exceptions?
  • Exceptions are errors that occur when the program is running.
  • They can be caused by various issues, such as incorrect input, missing files, or division by zero.
• Why Use Exceptions?
  • They help to manage errors without crashing the program.
  • They allow developers to provide user-friendly error messages and take corrective actions.

Exception Handling

• The try block lets you test a block of code for errors.
• The except block lets you handle the error if one occurs.
• In this example, if division by zero occurs, the program will not crash; instead, it will print a message.
  • The finally block can be used to execute code regardless of whether an exception occurred or not. It is often used for cleanup actions.

Finally Block

Example:

try:
    f = open("file.txt")
    # Process the file
except FileNotFoundError:
    print("File not found.")
finally:
    f.close()  # Ensures the file is closed

Try and Except Block

Example:

try:
    result = 10 / 0
except ZeroDivisionError:
    print("You can't divide by zero!")

Raising Exceptions

• You can raise exceptions manually using the raise keyword.
• This example raises a ValueError if the age is below 18.

def check_age(age):
    if age < 18:
        raise ValueError("Age must be 18 or older.")
        
try:
    check_age(15)
except ValueError as e:
    print(e)

Example:

Custom Exceptions

• You can create your own exceptions by subclassing the Exception class.

class MyCustomError(Exception):
    pass

raise MyCustomError("This is a custom error message.")

Example:

Conclusion

• Python exceptions are a powerful way to handle errors.
• Using try, except, finally, and custom exceptions helps create robust programs that can handle unexpected situations gracefully.