8 4 Raising Exceptions Explained

Key Concepts

Raising exceptions in Python involves several key concepts:

• What is an Exception?
• Why Raise Exceptions?
• How to Raise an Exception
• Custom Exceptions
• Handling Raised Exceptions

1. What is an Exception?

An exception is an event that occurs during the execution of a program that disrupts the normal flow of instructions. In Python, exceptions are objects that represent errors.

Analogy: Think of an exception as a red flag that signals something unexpected or wrong has happened in your program.

2. Why Raise Exceptions?

Raising exceptions allows you to explicitly signal that an error condition has occurred. This is useful for handling specific error scenarios and ensuring that your program behaves predictably.

Analogy: Think of raising an exception as a way to alert the user or the system that something needs attention, similar to a warning light on a dashboard.

3. How to Raise an Exception

In Python, you can raise an exception using the raise statement. You can raise built-in exceptions or create your own custom exceptions.

Example:

def divide(a, b):
    if b == 0:
        raise ZeroDivisionError("Cannot divide by zero")
    return a / b

try:
    result = divide(10, 0)
except ZeroDivisionError as e:
    print(e)
    

Analogy: Think of raising an exception as a way to stop the program and say, "Hey, something is wrong here!"

4. Custom Exceptions

You can create custom exceptions by defining a new class that inherits from the built-in Exception class. This allows you to handle specific error conditions in a more meaningful way.

Example:

class InvalidInputError(Exception):
    pass

def check_input(value):
    if value < 0:
        raise InvalidInputError("Input must be non-negative")

try:
    check_input(-5)
except InvalidInputError as e:
    print(e)
    

Analogy: Think of custom exceptions as creating your own warning signs tailored to specific situations in your program.

5. Handling Raised Exceptions

When an exception is raised, it can be caught and handled using a try-except block. This allows your program to recover gracefully from errors.

Example:

def safe_divide(a, b):
    try:
        return divide(a, b)
    except ZeroDivisionError as e:
        print("Error:", e)
        return None

result = safe_divide(10, 0)
print(result)
    

Analogy: Think of handling exceptions as having a contingency plan to deal with unexpected situations, ensuring your program can continue running smoothly.

Putting It All Together

By understanding and using these concepts effectively, you can manage exceptions in Python to create more robust and reliable programs.

Example:

class InvalidInputError(Exception):
    pass

def check_input(value):
    if value < 0:
        raise InvalidInputError("Input must be non-negative")

def divide(a, b):
    if b == 0:
        raise ZeroDivisionError("Cannot divide by zero")
    return a / b

def safe_divide(a, b):
    try:
        check_input(a)
        check_input(b)
        return divide(a, b)
    except (InvalidInputError, ZeroDivisionError) as e:
        print("Error:", e)
        return None

result = safe_divide(-10, 0)
print(result)