BUG: fix to_latex bold_rows option
State: closed

 - [x] closes #16707
 - [x] tests added / passed
 - [ ] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff``
 - [x] whatsnew entry


Labels:
name: Bug
name: IO LaTeX
description: to_latex

Comments:
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16708?src=pr&el=h1) Report
> Merging [#16708](https://codecov.io/gh/pandas-dev/pandas/pull/16708?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/3ff845b4e81d4dde403c29908f5a9bbfe4a87788?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/16708/graphs/tree.svg?token=eZ4WkYLtcO&height=150&width=650&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/16708?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16708      +/-   ##
==========================================
+ Coverage   90.91%   90.91%   +<.01%     
==========================================
  Files         161      161              
  Lines       49286    49288       +2     
==========================================
+ Hits        44810    44812       +2     
  Misses       4476     4476
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.69% <100%> (ø)` | :arrow_up: |
| #single | `40.17% <0%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16708?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/formats/format.py](https://codecov.io/gh/pandas-dev/pandas/pull/16708?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvZm9ybWF0LnB5) | `96.03% <100%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16708?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/16708?src=pr&el=footer). Last update [3ff845b...87ab246](https://codecov.io/gh/pandas-dev/pandas/pull/16708?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/16708?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@06fc667`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16708/graphs/tree.svg?token=eZ4WkYLtcO&width=650&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/16708?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #16708   +/-   ##
=========================================
  Coverage          ?   90.93%           
=========================================
  Files             ?      161           
  Lines             ?    49291           
  Branches          ?        0           
=========================================
  Hits              ?    44824           
  Misses            ?     4467           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.7% <100%> (?)` | |
| #single | `40.17% <0%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16708?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/16708?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `92.27% <ø> (ø)` | |
| [pandas/io/formats/format.py](https://codecov.io/gh/pandas-dev/pandas/pull/16708?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvZm9ybWF0LnB5) | `96.03% <100%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16708?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/16708?src=pr&el=footer). Last update [06fc667...a26bcb2](https://codecov.io/gh/pandas-dev/pandas/pull/16708?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

I had to adapt  the expected result of all existing tests where. to_latex() was used, as the default behaviour changed. I'm not so sure though whether it's a good idea to set bold_rows to True by default. I guess the reason for this documented  default is the analogy with. to_html(), but in that output also the column headers are bold. In addition, bold row and/or column headers do not seem very common in latex community examples. 
Could you show an example what the before/after output looks like rendered?  I'm inclined to agree that changing the default isn't a good idea.
With `bold_rows=False` (i.e. 'before' output):
![image](https://user-images.githubusercontent.com/1150402/27233171-daa1846a-52b8-11e7-9fdb-d9abb439e3b5.png)
With `bold_rows=True` (would be 'after' default output):
![image](https://user-images.githubusercontent.com/1150402/27233205-02a8be88-52b9-11e7-8c93-90b033b67907.png)

It's a matter of taste, but I don't like the latter one that much...

I'm in favor of keeping the default output the same as before, and correcting the signature (and docstring) of .to_latex() accordingly.
> I'm in favor of keeping the default output the same as before, and correcting the signature (and docstring) of .to_latex() accordingly.

+1
@jreback: As proposed, I made sure to have the same default behaviour as before (i.e. `bold_rows=False`) and corrected the `.to_latex()` signature accordingly.

I also added and updated a whatsnew entry as you asked, so I guess this is ready to be merged.
lgtm. can you rebase. ping on green. @TomAugspurger 
thanks!