Class 12 Exception Handling in Python: Notes and Quiz

Study Notes

Exception Handling in RBSE Class 12 Computer Science Chapter 1

Exception handling is a crucial aspect of programming that helps us manage and recover from unexpected, or exceptional, conditions in our code. In RBSE Class 12 Computer Science Chapter 1, we'll delve into this topic and explore its significance in ensuring robust and stable computer programs.

Background

Consider a scenario where you're writing a program that calculates the square root of a number, but the input might sometimes contain negative values. In this case, attempting to calculate the square root of a negative number would result in a ZeroDivisionError. By catching this exception and handling it, we can smoothly recover from the error and avoid program termination.

Exception Hierarchy

In Python, exceptions are organized in an inheritance hierarchy. This means that exceptions inheriting from a particular base class share similar characteristics and behavior. For example, ZeroDivisionError inherits from the ArithmeticError class, which in turn inherits from the Exception class.

Exception Handling Techniques

There are three primary techniques in Python for handling exceptions:

Try-except Blocks: This is a fundamental approach where we enclose the code block that might potentially raise an exception within a try block. Then, we specify the possible exceptions that could occur and define a corresponding except block to handle them.

try:
    # Code that might raise an exception
    # For example, calculating square root of a negative number
    square_root = math.sqrt(-5)
except ZeroDivisionError:
    # Handle the exception
    print("Can't calculate square root of a negative number.")

Raising Exceptions: In some cases, we might want to raise an exception ourselves instead of letting the Python interpreter do it. By using the raise keyword, we can explicitly throw an exception.
```
def divide_by_zero(dividend):
    if dividend == 0:
        raise ZeroDivisionError("Division by zero is not allowed!")
    return 1 / dividend
```

Exception Chaining: This technique allows us to link one exception to another, thereby providing a clear trace of the error and helping in debugging.

try:
    # Code that might raise an exception
    # For example, getting an email address from an incorrectly formatted string
    email_address = extract_email(incorrect_string)
except ValueError as exc_1:
    try:
        # Raise a specific email extraction error
        raise EmailExtractionError("Failed to extract email address.") from exc_1
    except Exception as exc_2:
        # If the extraction fails for some other reason (e.g., memory error)
        raise Exception("Exception occurred.") from exc_2

Best Practices

Be specific in your exception handling: Instead of catching generic exceptions like Exception or BaseException, catch only the specific exceptions you're anticipating. This helps maintain clear and concise exception handling code.
Handle exceptions at the point of their occurrence: Avoid catching exceptions in a higher level of the code if you're not going to handle them appropriately at that level.
Use descriptive exception names: Instead of using vague exception names like Error or Exception, create custom exceptions with descriptive names that explain their purpose and improve readability.
Don't let exceptions escape: Make sure to either handle an exception or let it be caught by a higher level of exception handling. Unhandled exceptions will lead to program termination.
Consider logging: Include logging in your exception handling code to track the error's occurrence and simplify debugging.

Conclusion

Exception handling is a fundamental concept in computer science that allows us to gracefully recover from unexpected, or exceptional, conditions in our code. By understanding and implementing techniques like try-except blocks, raising exceptions, and chaining exceptions, you can create robust and stable computer programs. Remember to follow best practices like being specific in your exception handling, handling exceptions at their point of occurrence, using descriptive exception names, and considering logging.

Reference(s):

Python's Official Tutorial on Errors and Exceptions.

Description

Explore the significance of exception handling in programming as covered in RBSE Class 12 Computer Science Chapter 1. Learn about exception hierarchy, handling techniques like try-except blocks and raising exceptions, best practices, and more.