[gpshead]

This refactors zipfile to add a register_compression() API and uses the API for all of our built-in stdlib based compressors (zlib's deflate, bz2, and lzma).

This allows additional compression methods to be officially supplied by third party libraries without monkeypatching the zipfile module. It is designed to obsolete the gross hacks that things like https://pypi.org/project/zipfile-zstd/ have to do.

Motivation: zstandard support in zipfile, without adding a zstandard implementation to the standard library and without using monkeypatching. But I'm sure others will find it useful as well. Another potential use case is enabling the use of optimized compressors (think parallelized zlib's like pigz) instead of the stdlib default implementations.

TODO items:

• Overall design review & feature discussions.
• Code review.
• Documentation (see the huge zipfile.register_compression docstring for now).
• NEWS entry & What's New text.

• Issue: Allow third party libraries to provide new zipfile compression methods #113767

[gpshead]

Some further deep diving on the API design and use here is needed. This refactoring and dancing around the decompressor flush method and differing APIs between zlib and bzip2 and lzma was frustratingly informative. #67389 should be considered and perhaps don't require a flush() on the decompressors at all?

[gpshead]

chatted with @emmatyping at the pycon US sprint today, she's going to take this on.

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[gpshead]

while the concept is still useful, we've gained compression.zstd in the stdlib so i'm not motivated to push this further.