REF: implement cumulative ops block-wise

[jbrockmendel]

• closes Cumulative Methods with mixed frames casts to object #19296
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

cc @TomAugspurger

[TomAugspurger]

Thanks.

Would be good to have a release note and some tests that exercise this directly.

[jreback]

ok with moving this later, does this need a whatsnew note / additional tests as @TomAugspurger asks?

[jbrockmendel]

does this need a whatsnew note / additional tests as

So far i haven't been able to write tests that fail without this. Haven't given up.

[jreback]

do @TomAugspurger original tests work on master?

[jbrockmendel]

do @TomAugspurger original tests work on master?

good point! no, but they work here. will update

[pep8speaks]

Hello @jbrockmendel! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2019-12-27 20:23:03 UTC

[jbrockmendel]

same unrelated-looking docbuild failure as #29847. im guessing this is going to be affecting all PRs about now, will take a look

[TomAugspurger]

Should be good to go.

[jreback]

thanks, looking forward to the cleanups!