CLN: Fix exception causes in datetimelike.py

[cool-RR]

• closes #xxxx
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[pep8speaks]

Hello @cool-RR! 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 2020-02-21 22:29:14 UTC

[jbrockmendel]

nitpick: can you make this "err" instead of "e"; i really dont like 1-letter names

[gfyoung]

Eh...I would leave it alone for this PR. I understand having an aesthetic preference, but e (as an exception variable name) is strewn all over the place in this file, and I don't see why we should nitpick this one instance and hold this PR up because of that.

If we have a generally accepted (for this repository) a stylistic preference for variable names for exceptions, then fine, but I'm not aware of that at this point.

[jbrockmendel]

yah, not a deal-breaker. i think of this as a "if you have to push another commit anyway, this would be nice"

[cool-RR]

Thanks for reviewing guys. I'm ambivalent towards the err change, so if you'd like me to change, I'll change it. If there's anything else I need to do about this PR, let me know.

[gfyoung]

Thanks @cool-RR, and welcome to pandas! 🎉

err naming question notwithstanding, it looks good!

[jbrockmendel]

@cool-RR is there something here we should be testing?

[cool-RR]

If you mean testing that the __cause__ attribute is set correctly, I think that's overkill. The only kind of testing that's useful is having test code that causes the exception, reaches the raise and ensures the correct exception gets raised, but that's orthogonal to this PR, i.e. it's needed about as much as it's needed without this PR.

[jbrockmendel]

sounds good, LGTM

[cool-RR]

Cool. Any next steps needed before merging?

[WillAyd]

I would be on board with doing this more generally if there's a way to identify easily

[WillAyd]

Thanks @cool-RR