Backports round 2
Hello @TomAugspurger! Thanks for updating the PR.







 - In the file [`pandas/core/internals.py`](https://github.com/pandas-dev/pandas/blob/37f954a43a01cc1c7f48e2e4f10fafe5d1996967/pandas/core/internals.py), following are the PEP8 issues :

> [Line 1843:13](https://github.com/pandas-dev/pandas/blob/37f954a43a01cc1c7f48e2e4f10fafe5d1996967/pandas/core/internals.py#L1843): [W503](https://duckduckgo.com/?q=pep8%20W503) line break before binary operator
> [Line 1895:13](https://github.com/pandas-dev/pandas/blob/37f954a43a01cc1c7f48e2e4f10fafe5d1996967/pandas/core/internals.py#L1895): [W503](https://duckduckgo.com/?q=pep8%20W503) line break before binary operator





















##### Comment last updated on December 11, 2017 at 21:06 Hours UTC Hmm, not sure why those linting errors are coming up here, but not in https://github.com/pandas-dev/pandas/pull/18385. Because W503 was added to setup.cfg as ignored error code on master See https://github.com/pandas-dev/pandas/pull/18046#discussion_r147925011. Maybe add a commit that adds it here as well and I merged https://github.com/pandas-dev/pandas/pull/18730 Ah thanks. Yes, I'll just make a new commit then I think. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18732?src=pr&el=h1) Report
> Merging [#18732](https://codecov.io/gh/pandas-dev/pandas/pull/18732?src=pr&el=desc) into [0.21.x](https://codecov.io/gh/pandas-dev/pandas/commit/8bede1ad6f467ad951ff7c3790d42223b5349b51?src=pr&el=desc) will **decrease** coverage by `0.03%`.
> The diff coverage is `70%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18732/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/18732?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           0.21.x   #18732      +/-   ##
==========================================
- Coverage   91.33%   91.29%   -0.04%     
==========================================
  Files         156      156              
  Lines       51807    51835      +28     
==========================================
+ Hits        47316    47322       +6     
- Misses       4491     4513      +22
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.17% <60%> (-0.03%)` | :arrow_down: |
| #single | `40.15% <30%> (-0.09%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18732?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/18732/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZWxpa2UucHk=) | `97.1% <100%> (ø)` | :arrow_up: |
| [pandas/io/formats/format.py](https://codecov.io/gh/pandas-dev/pandas/pull/18732/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvZm9ybWF0LnB5) | `96.1% <100%> (+0.14%)` | :arrow_up: |
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/pull/18732/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `94.47% <100%> (ø)` | :arrow_up: |
| [pandas/core/indexes/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/18732/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy90aW1lZGVsdGFzLnB5) | `91.15% <100%> (ø)` | :arrow_up: |
| [pandas/io/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/18732/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3B5dGFibGVzLnB5) | `92.84% <100%> (ø)` | :arrow_up: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/18732/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.57% <100%> (-0.1%)` | :arrow_down: |
| [pandas/io/parquet.py](https://codecov.io/gh/pandas-dev/pandas/pull/18732/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnF1ZXQucHk=) | `60.19% <60.86%> (-5.2%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18732/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18732/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.75% <0%> (-0.1%)` | :arrow_down: |
| ... and [1 more](https://codecov.io/gh/pandas-dev/pandas/pull/18732/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18732?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/18732?src=pr&el=footer). Last update [8bede1a...37f954a](https://codecov.io/gh/pandas-dev/pandas/pull/18732?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 lgtm.