*cough* You know, there's more to life than Python-X.Y.tar.gz :-). Not that I know how PendingDeprecationWarning is used in the wild. I've been thinking maybe we (numpy) should start using it for stuff that we want to discourage people from using (we know it was a bad idea or intrinsically broken or whatever), but don't yet have a full replacement to offer. It would help if there were some official guidance on what these things mean -- I can't find anything written down anywhere that even documents what you just said about how CPython proper uses them, so I imagine people have come up with all kinds of interpretations.

Anyway, my logic would be: when I am trying something out at the REPL, usually it is because I want to check how it works, to figure out what I should be doing in the real module code that I'm writing in the next window. When doing this, I definitely appreciate knowing that it will be removed and is being replaced -- it won't necessarily stop me from putting it into my code, but at least it's information that I can take into account.

I don't care a huge amount either way, though; if we decided to hide PendingDeprecationWarnings by default while showing DeprecationWarnings then numpy would just define a NumPyPendingDeprecationWarning subclass of DeprecationWarning and use that instead of PendingDeprecationWarning and all would work out fine :-).