Isn’t zlib only required for compression? It is my impression that zipfile’s decompressor is pure Python,
and only depends on zlib if the archive is encrypted (but wheels are never encrypted).

zlib also does not provide decompression at its core; for that you need zlib/contrib/minizip, but I don’t
think CPython depends on minizip either.

zlib is technically optional, and not even required to installed wheels.

On 05/9/2018, at 19:35, Donald Stufft <> wrote:

On Sep 4, 2018, at 6:06 AM, Alex Walters <> wrote:

Since zlib is a dependency of python, the assumption has to be that it is
already present.

It is technically an optional dependency of Python, though I don’t think you can install wheels without zlib present since wheels are zip files and generally include compression. Although maybe it could work in niche scenarios if someone built wheels using ZIP_STORED instead of ZIP_DEFLATE?
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