0.23.4 backports 1
Closes https://github.com/pandas-dev/pandas/issues/22166
> Closes #22166

@TomAugspurger : I thought we were experimenting with a bot that auto-backported?

Separate note: some weird `pytables` failures on Travis and Circle.  Not sure what happened but rerunning to confirm. > I thought we were experimenting with a bot that auto-backported?

Yes, tagging an issue with a milestone will automatically backport it if possible.

I think the whatsnew changes weren't tagged with the 0.23.4 milestone, because it contained changes that shouldn't be backported.

The window fix had a merge conflict. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22178?src=pr&el=h1) Report
> Merging [#22178](https://codecov.io/gh/pandas-dev/pandas/pull/22178?src=pr&el=desc) into [0.23.x](https://codecov.io/gh/pandas-dev/pandas/commit/6a0a95058659cec7515b0233d7795417dfb074fe?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22178/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/22178?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           0.23.x   #22178      +/-   ##
==========================================
+ Coverage   91.83%   91.83%   +<.01%     
==========================================
  Files         153      153              
  Lines       49592    49592              
==========================================
+ Hits        45541    45545       +4     
+ Misses       4051     4047       -4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.24% <ø> (ø)` | :arrow_up: |
| #single | `41.79% <ø> (-0.06%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22178?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/22178/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.24% <0%> (+0.05%)` | :arrow_up: |
| [pandas/core/panel.py](https://codecov.io/gh/pandas-dev/pandas/pull/22178/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcGFuZWwucHk=) | `97.32% <0%> (+0.44%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22178?src=pr&el=continue).
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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22178?src=pr&el=footer). Last update [6a0a950...7300fe7](https://codecov.io/gh/pandas-dev/pandas/pull/22178?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
