Let Calibre Use Locally Built Version of Dependency on Windows?

[mwgabby-li]

I wanted to test Calibre with some modifications to the css-parser library. What's the simplest way to have it use a version I have modified locally?

Bonus points if it can use the css-parser source tree directly, though I don't mind running the css-parser installer after modifying it.

[kovidgoyal]

Just prepend the path to it to sys.path before it is imported.

[mwgabby-li]

Thanks - that was part of the solution, but it wasn't working with just that. Just in case someone else needs to get this working, turns out I also had to modify sys.meta_path.

This is what I saw it as when Calibre is running. I guess the third entry in that list causes it to prioritize the built-in "frozen" libraries?:

sys.meta_path: [
<calibre.constants.DeVendor object at 0x000002128A2AA3A0>,
<__main__.PydImporter object at 0x000002128A22C310>,
BypyFrozenImporter with data in C:\Program Files\Calibre2\app\bin,
<class '_frozen_importlib.BuiltinImporter'>,
<class '_frozen_importlib.FrozenImporter'>,
<class '_frozen_importlib_external.PathFinder'>,
<calibre.constants.ExtensionsImporter object at 0x000002128A2B11F0>
]

To get it working quickly, in addition to modifying sys.path to have css-parser/src listed first before all imports using that module, I just did this in constants.py after the DeVendor() and ExtensionsImporter() are added:

sys.meta_path.insert(0, sys.meta_path[5])

I daresay there's probably a more elegant solution to this, but there you are.