Our first priority should be that we shouldn't need to write comments in our code. The code should be clean enough (i.e. naming conventions, formatting, functions, etc) that it should self explain when looked at. But there are some cases where we might wanna consider writing comments.

Implementing the principles of good and bad comments in code requires careful consideration of clarity, necessity, and maintainability.

When writing code, it's best to make it easy to understand without needing lots of comments. This means using clear names for things and organizing the code in a logical way. Comments should only be used when necessary, like when something isn't obvious from the code alone.

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Poor Comments

1. Redundant Comments:-

    # Increment x by 1
    x += 1
   

   Comments like this are redundant because the code itself is self-explanatory and adding a comment doesn't provide any additional value.

2. Misleading Comments:-

    # Calculate average of numbers
    total = sum(numbers)
   

   Misleading comments can confuse other developers and lead to misunderstandings about the code's functionality. Like the above example has a comment that says 'Calculate average of numbers'. But actually, it's summing the numbers, not calculating the average.

3. Commented-out Code:-

    # x = 10
    # This line is commented out because we're not sure if we still need it.
   

   Leaving commented-out code in the source can clutter the codebase and make it difficult to understand the active code.

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Good Comments

1. Legal Information:-

    # Copyright (C) 2024 CompanyXYZ. All rights reserved.
   

   This type of comment provides important legal information about the code's ownership and usage rights.

2. Explanations which can't be replaced by naming convention:-

    # Explanation: Using a custom sorting algorithm due to specific requirements.
    def custom_sort(items):
        # Custom sorting algorithm implementation
        pass
   

   In this case, the comment explains why a custom sorting algorithm is being used instead of a built-in sorting function. This explanation provides valuable context that cannot be conveyed solely through the function name or code itself.

3. Warnings:-

    # WARNING: This function modifies the global variable 'counter'.
    def increment_counter():
        global counter
        counter += 1
        return counter
   

   In this example, the comment warns other developers that the function increment_counter() modifies a global variable named counter. This information is crucial for understanding the potential side effects of using this function.

4. Todo:-

    # TODO: Implement error handling for invalid input.
    def parse_input(input_str):
        # Code for parsing input goes here
        pass
   

   Here, the comment indicates that the function parse_input() lacks error handling for invalid input. This serves as a reminder to implement this functionality in the future.

5. Documentation Comments:-

    """
    This function calculates the area of a rectangle.
   
    :param length: The length of the rectangle.
    :param width: The width of the rectangle.
    :return: The area of the rectangle.
    """
    def calculate_rectangle_area(length, width):
        return length * width
   

   Documentation comments provide comprehensive documentation for functions, classes, or modules, enhancing code readability and maintainability.

In short, good code speaks for itself. By keeping things clear and organized, we can avoid the need for too many comments. While comments have their place, we should aim for code that's easy to understand without them. If used, comments should add value by providing necessary context, warnings, or documentation, rather than stating the obvious or cluttering the code base with redundant or misleading information.