Use either brotli or brotlicffi.

[lovelydinosaur]

See #1605 (comment)

• The brotli package is recommended for CPython.
• The brotlicffi package is recommended for PyPy.

Note the following:

• We have to use Decompressor.decompress if brotlicffi is installed, but Decompressor.process if brotli is installed.
• We can use Decompressor.finish() if brotlicffi is installed.
• We use the oddly-cased brotli.error instead of brotli.Error because it is supported as a synonym in both packages.

Also worth calling out the the older brotlipy package might be installed on the system. In which case it will shadow the brotli package namespace. Ug.

[j178]

I thinkbrotlicffi also has a process alias for decompress:

https://github.com/python-hyper/brotlicffi/blob/68c0431673e6c59549079e6588b043a707262c80/src/brotlicffi/_api.py#L423

How about just use self.decompressor.process?

[lovelydinosaur]

True. Tho I double checked and the brotlipy package doesn't, so what we want to do here depends on if we want to take care around the possibility that on some systems the older brotlipy package might have been installed. (Or not.)

• If we do care about that awkward case, then we should just update the comment strings here.
• If we don't case about that case, then we should just always use Decompressor().process().

Perhaps we could check which of brotli vs brotlipy is installed the _compat.py module, and raise an error if brotlipy is installed and is shadowing the brotli namespace.

For example:

    if hasattr(brotli.Decompressor, 'decompress'):
        raise RuntimeError(
            "The brotlipy library appears to be installed, and is shadowing the 'brotli' namespace. "
            "Uninstall brotlipy and use brotlicffi instead."
        )