Backport PR #24916 on branch 0.24.x (BUG-24212 fix regression in #24897)
Backport PR #24916: BUG-24212 fix regression in #24897
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=h1) Report
> Merging [#24951](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=desc) into [0.24.x](https://codecov.io/gh/pandas-dev/pandas/commit/31dcbb75dbcd315af9baf4ff9bd25cbf483046c0?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24951/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           0.24.x   #24951      +/-   ##
==========================================
+ Coverage   92.37%   92.38%   +<.01%     
==========================================
  Files         166      166              
  Lines       52388    52398      +10     
==========================================
+ Hits        48396    48406      +10     
  Misses       3992     3992
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <100%> (ø)` | :arrow_up: |
| #single | `42.89% <8.33%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/reshape/merge.py](https://codecov.io/gh/pandas-dev/pandas/pull/24951/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9tZXJnZS5weQ==) | `94.48% <100%> (+0.07%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=footer). Last update [31dcbb7...24c6164](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=h1) Report
> Merging [#24951](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=desc) into [0.24.x](https://codecov.io/gh/pandas-dev/pandas/commit/31dcbb75dbcd315af9baf4ff9bd25cbf483046c0?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24951/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           0.24.x   #24951      +/-   ##
==========================================
+ Coverage   92.37%   92.38%   +<.01%     
==========================================
  Files         166      166              
  Lines       52388    52398      +10     
==========================================
+ Hits        48396    48406      +10     
  Misses       3992     3992
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <100%> (ø)` | :arrow_up: |
| #single | `42.89% <8.33%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/reshape/merge.py](https://codecov.io/gh/pandas-dev/pandas/pull/24951/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9tZXJnZS5weQ==) | `94.48% <100%> (+0.07%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=footer). Last update [31dcbb7...24c6164](https://codecov.io/gh/pandas-dev/pandas/pull/24951?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jreback I reverted this *on the 0.24.x branch*, see my comments there (https://github.com/pandas-dev/pandas/pull/24916#pullrequestreview-196792659), I feel this has a bit a too big possibility on side effects to include it in a bug fix release (it's also not a critical bug fix anyway). @jorisvandenbossche ]please speak up much sooner then

i would rather not have this kind of back and forth

actually, pls discuss in the future before you do that. 

> it's also not a critical bug fix anyway).

is not true, this actually is a valid backport. @jreback I *did* speak up before you merged this: https://github.com/pandas-dev/pandas/pull/24916#issuecomment-457837974 and https://github.com/pandas-dev/pandas/pull/24916#pullrequestreview-196792659 no you didn’t  @jorisvandenbossche I am not sure why you didn't change the what's new in 0.25.0 as well here. This is likely to cause merging issues to 0.24.x. can you update that. What looks wrong about the 0.25.0.rst on the 0.24.x branch? I don't see any issues. As long as it has the orphan directive and isn't in the whatsnew/index.rst toctree, thing should be fine. https://github.com/pandas-dev/pandas/blob/master/doc/source/whatsnew/v0.24.1.rst

has the change, but should be in 0.25.0 👍 https://github.com/pandas-dev/pandas/pull/24998 Yeah, I didn't do that yet, was on my to do list. See https://github.com/pandas-dev/pandas/pull/24999 Whoops, sorry was doing that at the same time :)