provide temp flag for outside libs to detect multi-backend preview

[Titus-von-Koeller]

After internal discussion how to handle this Transformers issue that came up when trying to test the alpha release in conjunction with the HF ecosystem, this is a simple approach that could help outside libs detect if they're dealing with the BNB preview version.

Wdyt @younesbelkada @akx @matthewdouglas ?

Hmm, maybe setting it to True is cleaner.. Thought of the str before adding the extensive comment..

Added this snippet to bnb/__init__.py:

# NOTE: this is a temporary flag to allow outside libraries to employ conditional logic while the refactor is still in
# alpha/beta: sth like `if getattr(bitsandbytes, "is_multi_backend_refactor_preview", False): do sth`
# the getattr() call above would default to False and any string evaluates to True. This way we have temporary thing
# that we can remove in Transformers with the next release after the official BNB multi-platform release; then
# eventually making it the new default (e.g. just remove if statement and dedent in Transformers)
is_multi_backend_refactor_preview = "TO BE REMOVED ONCE MERGED TO `main`"  # bool evals to True for str

In [1]: import bitsandbytes as bnb

In [2]: bnb.is_multi_backend_refactor_preview
Out[2]: 'TO BE REMOVED ONCE MERGED TO `main`'

In [3]: bool(getattr(bnb, "is_multi_backend_refactor_preview", False))
Out[3]: True

In [4]: del bnb.is_multi_backend_refactor_preview  # not defined on `main`

In [5]: getattr(bnb, "is_multi_backend_refactor_preview", False)
Out[5]: False

[younesbelkada]

Thanks a lot !

[akx]

If we wanted to make this a more permanent feature (and I don't see why not), it could just be e.g. features = {"multi_backend"}...