ops cleanup, named functions instead of lambdas
Lots more ops work in the pipeline, this is just the easy bits that don't need new tests.

Having reversed funcs that can be referenced will make things easier in some of the Index classmethods.
Hello @jbrockmendel! Thanks for updating the PR.



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

##### Comment last updated on February 03, 2018 at 00:27 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19515?src=pr&el=h1) Report
> Merging [#19515](https://codecov.io/gh/pandas-dev/pandas/pull/19515?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/69cd5fbfd8b57033b0eb280ebc6dd502652f269c?src=pr&el=desc) will **decrease** coverage by `0.1%`.
> The diff coverage is `84%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19515/graphs/tree.svg?token=eZ4WkYLtcO&width=650&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/19515?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19515      +/-   ##
==========================================
- Coverage   91.69%   91.59%   -0.11%     
==========================================
  Files         148      150       +2     
  Lines       48561    48705     +144     
==========================================
+ Hits        44530    44612      +82     
- Misses       4031     4093      +62
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.96% <84%> (-0.1%)` | :arrow_down: |
| #single | `41.75% <64%> (+0.03%)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19515?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/19515/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvb3BzLnB5) | `95.22% <84%> (-0.52%)` | :arrow_down: |
| [pandas/errors/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/19515/diff?src=pr&el=tree#diff-cGFuZGFzL2Vycm9ycy9fX2luaXRfXy5weQ==) | `92.3% <0%> (-7.7%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/19515/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.22% <0%> (-1.74%)` | :arrow_down: |
| [pandas/core/arrays/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/19515/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2NhdGVnb3JpY2FsLnB5) | `94.74% <0%> (-1.04%)` | :arrow_down: |
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/pull/19515/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `95.05% <0%> (-0.42%)` | :arrow_down: |
| [pandas/core/dtypes/dtypes.py](https://codecov.io/gh/pandas-dev/pandas/pull/19515/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2R0eXBlcy5weQ==) | `96.08% <0%> (-0.04%)` | :arrow_down: |
| [pandas/core/arrays/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/19515/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL19faW5pdF9fLnB5) | `100% <0%> (ø)` | :arrow_up: |
| [pandas/core/arrays/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/19515/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2Jhc2UucHk=) | `56.66% <0%> (ø)` | |
| [pandas/core/dtypes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/19515/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Jhc2UucHk=) | `47.61% <0%> (ø)` | |
| [pandas/core/dtypes/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/19515/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2NvbW1vbi5weQ==) | `95.37% <0%> (+0.05%)` | :arrow_up: |
| ... and [1 more](https://codecov.io/gh/pandas-dev/pandas/pull/19515/diff?src=pr&el=tree-more) | |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19515?src=pr&el=footer). Last update [69cd5fb...e39ad01](https://codecov.io/gh/pandas-dev/pandas/pull/19515?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!