Changing package import logic

[rtobar]

This issue is to change the package's import logic. At the moment the package fails to import in platforms where no hardware support is found (i.e., anything other than Intel SSE4.2-capable CPUs) unless an environment variable, specified beforehand, instructs the package to expose its software implementation instead.

This package initially contained only an Intel-based crc32c implementation, but with time a software implementation was incorporated but the importing logic was maintained for backwards compatibility. With the advent of the software implementation (#4) the importing logic has been highlighted as being not necessarily ideal (#5 and #11).

An improved logic, and what most users seem to expect, would work as follow: by default a hardware-based implementation would be offered. If this cannot be offered, the software implementation would be offered instead. This way the package would never fail to import. This would imply that the CRC32C_SW_MODE variable would become deprecated (we could issue such a deprecation warning upon seeing it). Additionally I would still like it to be clear when a hardware implementation is exposed and when not -- maybe this can be done by attaching an attribute to the crc32c function, or at the package level. This way people relying on a fast, hardware-based implementation can still check if this is the case and act accordingly.

Since this would be a breaking change (with not too grave consequences though), this would need a bump on the package's major version.

[ossdev07]

Hi @rtobar ,
Thanks for picking up on this issue so early.
How soon can we expect a release with the necessary changes ? Any tentative timeline ?

[rtobar]

I probably won't be pressing too hard on this on the near future -- say until December or so, but who knows. I created the ticket more as a reminder to do it, not necessarily because I was planning to do it soon.

I'm happy to review PRs though, along the lines of what I described above.

[rtobar]

BTW, until this is implemented something like the following be used to avoid import errors:

import os

os.environ['CRC32C_SW_MODE'] = 'auto'
import crc32c

[rtobar]

A first version of the new logic is now available in the master branch. Now the software implementation is used by default as a fallback, unless the CRC32C_SW_MODE environment variable is set to none, in which case the old behavior takes place.

@ossdev07 please have a try and let me know how this works for you. After some more testing I'll be cutting a new crc32c version (probably next week though) with this change.

[rtobar]

crc32c version 2.0 now released in PyPI contains this change, closing issue now.