On Nov 19, 2017, at 8:40 AM, Nathaniel Smith <njs@pobox.com> wrote:
We have been using DeprecationWarning for changes where code will transition from working -> raising an error, and that *is* based on the Official Recommendation to hide those by default whenever possible. We've been doing this for a few years now, and I'd say our experience so far has been... poor. I'm trying to figure out how to say this politely. Basically it doesn't work at all. What happens in practice is that we issue a DeprecationWarning for a year, mostly no-one notices, then we make the change in a 1.x.0 release, everyone's code breaks, we roll it back in 1.x.1, and then possibly repeat several times in 1.(x+1).0 and 1.(x+2).0 until enough people have updated their code that the screams die down. I'm pretty sure we'll be changing our policy at some point, possibly to always use FutureWarning for everything.
In pip we ended up working around the not-displaying-by-default so that we got the old behavior back again because hiding warnings doesn’t work great in my experience.