[Tim Peters]
Note: sometimes _internals_ use deprecated gimmicks in order to support deprecated gimmicks too, and then stacklevel=3 is too small. It's happened so rarely in ZODB that I haven't tried to "do something" about that yet.
[Chris Withers]
Interestingly, I've found that even this is sometimes not enough, since you don't know whether you want the caller, the caller's caller or further up the chain than that.
I haven't seen much of that. One place I did is in deprecating subtransactions, where many paths thru the ZODB code have to pass on the original "is this a sub or a 'real' transaction?" flag. In those cases, the relevant methods also grew an optional `deprecation_wng` argument defaulting to True, and _internal_ calls to such methods explicitly pass "deprecation_wng=False".
Is there any way to get the warnings stuff to actually emit a traceback so it can be followed?
No; the `warnings` module doesn't even import the `traceback` module, let alone use it. You can print a traceback yourself by using the `traceback` module, and if you're determined enough you could replace warnings.showwarning() with a function of your own (see the docs for warnings.showwarning, and possible for traceback.print_stack).