COMPAT: implement visit_Constant for 3.8 compat
Closes https://github.com/pandas-dev/pandas/issues/27261

xref https://bugs.python.org/issue32892

Do we plan to do a 0.25.2, or keep open the option? (basically meaning: do we keep backporting for now?) If so, this would be a candidate I think. would be +1 on. potential 0.25.2 esp if we can have 3.8 support in it According to https://www.python.org/dev/peps/pep-0569/, the release date is targeted for October 21.

I'm not sure we'll get 1.0 out by then so a (conservative) 0.25.2 makes sense. Just plan to backport 3.8 fixes and 0.25 regressions? FYI, I need to read through https://bugs.python.org/issue36917 a bit more to make sure this is a valid fix. So consider this WIP for now. Once we get to 3.8 as a minimum we could get rid of the other types represented here right? If so maybe worth a comment of some sort Updated with all the tests that were failing for me locally with 3.8.

Note that we can't test against 3.8 beta3 because a segfault would crash the test workers (I think). That's fixed in https://github.com/python/cpython/pull/15390 which will be in beta 4. > Once we get to 3.8 as a minimum we could get rid of the other types represented here right? If so maybe worth a comment of some sort

I'm not sure exactly which ones can be removed once 3.8 is our min version. I don't think I understand this code / the changes well enough to say. Sounds good. Can cross that bridge when we get there Unless someone else has objections I so go ahead and merge