BUG: Index.str.partition not nan-safe (#23558)
State: closed

- [x] closes #23558 and 
closes #23677
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`


Labels:
name: Bug
name: Indexing
description: Related to indexing on series/frames, not to indexes themselves
name: Missing-data
description: np.nan, pd.NaT, pd.NA, dropna, isnull, interpolate
name: Strings
description: String extension data type and string data

Comments:
Hello @meiermark! Thanks for updating the PR.

 - There are no PEP8 issues in the file [`pandas/tests/test_strings.py`](https://github.com/meiermark/pandas/blob/25e3cc46537a5f3f9ef6fc265d0847c9cf422177/pandas/tests/test_strings.py) !



##### Comment last updated on November 18, 2018 at 01:05 Hours UTC
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23618?src=pr&el=h1) Report
> Merging [#23618](https://codecov.io/gh/pandas-dev/pandas/pull/23618?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/1250500cfe18f60cfb8a4867c82d14467bbee7ad?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/23618/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23618?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23618   +/-   ##
=======================================
  Coverage   92.23%   92.23%           
=======================================
  Files         161      161           
  Lines       51408    51408           
=======================================
  Hits        47416    47416           
  Misses       3992     3992
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.62% <ø> (ø)` | :arrow_up: |
| #single | `42.3% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23618?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/23618?src=pr&el=footer). Last update [1250500...4a20094](https://codecov.io/gh/pandas-dev/pandas/pull/23618?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

cc @h-vetinari if you want to have a look.
@jreback @meiermark 

Not sure if this is closed intentionally or permanently. It's a valid proposal to change the output of `to_object_array_tuples`, but primarily, the problem should be tackled through the MultiIndex constructor, which is the actual problem for `.str.partition`, see #23578. I've got a solution already as part of #23167, but this is currently blocked by / waiting for #23582.
Sorry for the confusion. I destroyed my branch and needed to restore it. Unfortunately, the pull request was closed by this.
@jreback The whatsnew info was added with the last commit.
@meiermark 
This should very likely also solve #23677. Could you have a look, and maybe adapt the tests accordingly as well?
@h-vetinari I extended some tests to check #23677. Your assumption was right, it's also resolved.
@jreback can you have a look again? The current state should include the required changes.
does this close both issues at the top of the PR? can you annotate a test where they are covered. also add to the whatsnew both issue numbers.
@jreback Yes, this PR closes both issues. Added comments to the tests (links to the corresponding issues) and a new whatsnew message.
thanks @meiermark keep em coming!