BUG: Fix line_terminator option
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Hello @BenRussert! Thanks for updating the PR.



Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on January 16, 2019 at 06:09 Hours UTC [This line](https://github.com/pandas-dev/pandas/blob/4dbf05d69d55d1ec86e467ef75acf4eb9f406273/pandas/io/formats/csvs.py#L72) won't ever reach 'os.linesep' if the default argument is '\n'. I noticed the issue because windows to_csv, and to_clipboard write `\n` when the docs indicate the default windows `\r\n`

I've only tried the tests locally on ubuntu, but I wonder if this will break tests for people running on windows if `\n` is hardcoded in the test. (I'll look later if this makes sense) # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23608?src=pr&el=h1) Report
> Merging [#23608](https://codecov.io/gh/pandas-dev/pandas/pull/23608?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/33f91d8f9f2e84f2b5f3ac3f0481b691c977c427?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23608/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23608?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23608   +/-   ##
=======================================
  Coverage   92.38%   92.38%           
=======================================
  Files         166      166           
  Lines       52358    52358           
=======================================
  Hits        48373    48373           
  Misses       3985     3985
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.81% <ø> (ø)` | :arrow_up: |
| #single | `43.07% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/23608?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/formats/csvs.py](https://codecov.io/gh/pandas-dev/pandas/pull/23608/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvY3N2cy5weQ==) | `98.22% <ø> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23608?src=pr&el=continue).
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> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23608?src=pr&el=footer). Last update [33f91d8...9897a49](https://codecov.io/gh/pandas-dev/pandas/pull/23608?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @BenRussert : Good start!  Definitely going to need some tests. @BenRussert can you add some tests for this I've added tests @gfyoung and @jreback, sorry for the delay!

I also found an issue! This closes #11720 See also #20353, #11720. to_csv issue was fixed in #21406, but the issue remains for windows users in `to_clipboard`. is there an associated issue? > is there an associated issue?

#11720 describes the behavior (which may have been fixed by #24290). There's also at least one or two other issues out there that can be closed. can you merge master > can you merge master

@jreback DId you want me to push a merge commit? Or rebase and force? the former @BenRussert can you update your OP to reflect which issue this addresses? Somewhat confused reading through the comments as to what problem this solves I'll just close and say that #24290 fixed what I was going after. The default argument vs calling with `None` is what confused me.