Catch correct parse errror type for dateutil >= 2.8.1

[timhoffm]

PR Summary

Fixes #15726.

Backporting to 2.2.5 because dateutil 2.8.1 still supports Python 2.

Release critical because this execption is part of a standard code path (_str_is_convertible() returning False).

[anntzer]

That looks like a bug in dateutil? (the exception is raised while trying to format the message for the actual exception...) Let's see whether @pganssle plans to fix that soon, if there's an (e.g.) 2.8.1.1 that fixes it perhaps we can just not support 2.8.1.

[pganssle]

I don't think this has been reported, do you have any details about how to trigger this?

[anntzer]

traceback is at #15726, sorry I don't have a minimal repro but the last line of the tb is

~/anaconda3/envs/pylandstats/lib/python3.6/site-packages/dateutil/parser/_parser.py in parse(self, timestr, default, ignoretz, tzinfos, **kwargs)
    655             ret = self._build_naive(res, default)
    656         except ValueError as e:
--> 657             six.raise_from(ParserError(e.args[0] + ": %s", timestr), e)
    658 
    659         if not ignoretz:

TypeError: unsupported operand type(s) for +: 'int' and 'str'

[pganssle]

Created an issue in dateutil/dateutil#981.

Shouldn't be too tough to fix it.

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout v2.2.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 026dacd2cb90dc6b2cf17a8edafda213f51cb7c6

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #15729: Catch correct parse errror type for dateutil >= 2.8.1'

4. Push to a named branch :

git push YOURFORK v2.2.x:auto-backport-of-pr-15729-on-v2.2.x

5. Create a PR against branch v2.2.x, I would have named this PR:

"Backport PR #15729 on branch v2.2.x"

And apply the correct labels and milestones.

Congratulation you did some good work ! Hopefully your backport PR will be tested by the continuous integration and merged soon!

If these instruction are inaccurate, feel free to suggest an improvement.

[timhoffm]

Doesn't need backport to 2.2.x because that code path did not exist there yet.