Understanding the NONE Object: A Deep Dive into SCons Custom Dependency Scanners

Описание: Discover why your SCons custom dependency scanner returns a `NONE` object, and learn how to make it more descriptive for better debugging and clarity.
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This video is based on the question https://stackoverflow.com/q/62946778/ asked by the user 'Vimal Patel' ( https://stackoverflow.com/u/8272206/ ) and on the answer https://stackoverflow.com/a/62947110/ provided by the user 'bdbaddog' ( https://stackoverflow.com/u/82681/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the NONE Object: A Deep Dive into SCons Custom Dependency Scanners

When working with SCons, a powerful build automation tool in Python, you may encounter a puzzling situation: your custom dependency scanner returns a NONE object. If you've found yourself in this scenario, this post will clarify why this happens and guide you on how to resolve it.

The Problem: dscanner Returns None

In your SConscript file, you may define a custom dependency scanner like this:

[[See Video to Reveal this Text or Code Snippet]]

However, when you print dscanner, it unexpectedly returns None. This can be frustrating, especially when you're trying to debug your build process. To understand what's happening, we need to dig a little deeper into the SCons API.

The Solution: Understanding Scanner Objects

SCons API Oddity: The "NONE" Attribute

As explained by a community contributor, this behavior is not a bug but rather a quirk of the SCons API. Here’s what you need to know:

The default name attribute of a scanner object in SCons is "NONE".

When you call str() or print the scanner object, it outputs NONE, leading to the confusion.

Providing a Descriptive Name

To avoid this confusion and make your scanners easier to understand, you can provide a more descriptive name when constructing your Scanner object. Here’s how to modify your code:

[[See Video to Reveal this Text or Code Snippet]]

With the addition of name='CustomScanner', your output will now reflect the custom name, helping you quickly identify what dscanner represents during debugging.

Key Takeaways

Understanding the NONE Output: It’s primarily related to the default behavior of the SCons API, not an error in your code.

Customize Your Scanner’s Name: Providing a unique name can significantly enhance clarity when reviewing outputs or debugging your build scripts.

Conclusion

Understanding the behavior of your tools is essential for effective programming and debugging. If your SCons custom dependency scanner is returning NONE, remember that this is a standard output linked to the SCons API's design. By naming your scanner descriptively, you not only resolve the confusion but also improve your code's readability and maintainability.

Feel free to reach out if you have further questions or need more clarity on SCons or dependency scanning!