Use black 19.10b0
- [x] closes #29341
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Main differences can be found on the 19.10 changelog:

https://black.readthedocs.io/en/stable/change_log.html
> Might be nice explicitly specify the version of `black` in the `.pre-commit-config.yaml`:
> 
> https://github.com/pandas-dev/pandas/blob/9bbb5f00c8396e5d7142eb973243c191e553c525/.pre-commit-config.yaml#L2-L6
> 
> Just a matter of modifying `stable` --> `19.10b0`

Good point - done! > this is backward incompatible? pls update the contributing guide as well

Added a note in contributing guide.

Correct - backwards incompatible. i.e Running an older version will undo some of the changes here.

Examples of the backwards incompatible issues can be found here:
https://github.com/psf/black/issues/1139
 can you merge master.

@TomAugspurger @jorisvandenbossche 

so this will force the new black in development. I *think* we are ok with this as its a dev dep. SGTM

On Mon, Nov 11, 2019 at 8:36 AM Jeff Reback <notifications@github.com>
wrote:

> can you merge master.
>
> @TomAugspurger <https://github.com/TomAugspurger> @jorisvandenbossche
> <https://github.com/jorisvandenbossche>
>
> so this will force the new black in development. I *think* we are ok with
> this as its a dev dep.
>
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 Merged master and addressed final comments. @jorisvandenbossche in reply to your comment:

I was surprised that black doesn't support this - I upvoted -> psf/black#790

I hope they will address this soon psf/black#1139 Anything else needed here @jreback @jorisvandenbossche ? can you see if there is going to be a forthcoming releases in black. some of these changes *might* be reverted. I don't have a problem with fixing the version of black that we are using. but we shouldn't churn unecessarily. > can you see if there is going to be a forthcoming releases in black. some of these changes _might_ be reverted. I don't have a problem with fixing the version of black that we are using. but we shouldn't churn unecessarily.

Sure it seems there will be a stable black release in 2019 (no more betas) - according to @ambv - [here](https://twitter.com/llanga/status/1187675968007278592).

https://github.com/psf/black/issues/1139 isn't fixed on black master yet though - I imagine the only the changes made here that __may__ be revert are to `test_callable.py` and `test_array.py` 
 I am fine with merging this now, it's only a small change that we might need to revert again Hello @alimcmaster1! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:









































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

##### Comment last updated at 2019-11-17 14:43:16 UTC Merged master and green. cc @jreback  thanks @alimcmaster1 