On Fri, Aug 24, 2018 at 1:36 AM Hameer Abbasi <einstein.edison@gmail.com> wrote:

On Fri, Aug 24, 2018 at 9:38 AM Nathaniel Smith <njs@pobox.com> wrote:
On Thu, Aug 23, 2018 at 9:02 AM,  <einstein.edison@gmail.com> wrote:
> I might add that most duck array authors are highly unlikely to be newcomers
> to the Python space. We should just put a big warning there while enabling
> and that’ll be enough to scare away most devs from doing it by default.

That's a reasonable idea... a Big Obnoxious Warning(tm) when it's
enabled, or on first use, would achieve a lot of the same purpose.

if this_is_the_first_array_function_usage():
        "WARNING: this program uses NumPy's experimental
'__array_function__' feature.\n"
        "It may change or be removed without warning, which might
break this program.\n"
        "For details see


I was thinking of a FutureWarning... That's essentially what it's for. Writing to stderr looks un-pythonic to me.

Issuing a FutureWarning seems roughly appropriate here. The Python 3.7 docs write:
"Base category for warnings about deprecated features when those warnings are intended for end users of applications that are written in Python."

Writing to sys.stderr directly is generally considered poor practice for a Python libraries.

In my experience FutureWarning does a good job of satisfying the goals of being a "Big Obnoxious Warning" while still being silence-able and testable with standard tools.