Error Handling and Exceptions in Python

1. Custom Exceptions

In Python, you can create your own custom exceptions by defining a new class that inherits from the built-in Exception class. This allows you to create exceptions that are more meaningful for your specific application.

Creating a Custom Exception Class

Here's an example of a custom exception class:

class NegativeValueError(Exception):
    """Exception raised for errors in the input if the input value is negative."""
    def __init__(self, value):
        self.value = value
        self.message = f"Negative value encountered: {self.value}"
        super().__init__(self.message)

# Example usage
def calculate_square_root(value):
    if value < 0:
        raise NegativeValueError(value)
    return value ** 0.5

try:
    result = calculate_square_root(-9)
except NegativeValueError as e:
    print(e)  # Expected output: Negative value encountered: -9

2. Best Practices for Error Handling

When handling errors in Python, follow these best practices:

• Use Specific Exceptions: Catch specific exceptions instead of using a general except clause. This improves code clarity and prevents hiding unexpected errors.
• Avoid Silent Failures: Always log or print error messages to understand what went wrong. Silent failures can make debugging difficult.
• Keep Try Blocks Small: Only include code that may raise an exception within the try block. This makes it clear what code is being protected from exceptions.
• Clean Up Resources: Use the finally block or context managers (with the with statement) to ensure that resources are released, regardless of whether an exception occurred.

3. Example: Custom Exception Usage

Let's take a look at an example that uses our NegativeValueError custom exception:

def main():
    values = [4, -16, 9]
    for value in values:
        try:
            sqrt = calculate_square_root(value)
            print(f"The square root of {value} is {sqrt}")
        except NegativeValueError as e:
            print(f"Error: {e.message}")

# Call the main function
main()

This example will iterate over a list of values, attempting to calculate their square roots. When it encounters a negative value, it raises a NegativeValueError and prints an error message instead of terminating the program.

4. Summary

In this tutorial, we explored error handling in Python, focusing on custom exceptions and best practices for using try-except blocks. By creating custom exceptions, you can provide clearer error handling in your applications, improving the overall robustness and readability of your code.