DOC: remove imports and use pd in docstrings
looks like this is not rebase on master

can you do

``git merge master`` @jreback .. ok.. will do! # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21797?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@9e1f6fd`). [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/21797/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/21797?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #21797   +/-   ##
=========================================
  Coverage          ?   91.95%           
=========================================
  Files             ?      160           
  Lines             ?    49858           
  Branches          ?        0           
=========================================
  Hits              ?    45845           
  Misses            ?     4013           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.33% <100%> (?)` | |
| #single | `42.08% <100%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21797?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/sparse/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/21797/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3BhcnNlL3Nlcmllcy5weQ==) | `95.2% <ø> (ø)` | |
| [pandas/plotting/\_misc.py](https://codecov.io/gh/pandas-dev/pandas/pull/21797/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19taXNjLnB5) | `38.98% <ø> (ø)` | |
| [pandas/core/window.py](https://codecov.io/gh/pandas-dev/pandas/pull/21797/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvd2luZG93LnB5) | `96.28% <ø> (ø)` | |
| [pandas/io/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/21797/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3B5dGFibGVzLnB5) | `92.48% <ø> (ø)` | |
| [pandas/core/resample.py](https://codecov.io/gh/pandas-dev/pandas/pull/21797/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzYW1wbGUucHk=) | `96.07% <ø> (ø)` | |
| [pandas/core/dtypes/dtypes.py](https://codecov.io/gh/pandas-dev/pandas/pull/21797/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2R0eXBlcy5weQ==) | `95.98% <ø> (ø)` | |
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/21797/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.63% <ø> (ø)` | |
| [pandas/core/arrays/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/21797/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2NhdGVnb3JpY2FsLnB5) | `95.93% <ø> (ø)` | |
| [pandas/core/algorithms.py](https://codecov.io/gh/pandas-dev/pandas/pull/21797/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYWxnb3JpdGhtcy5weQ==) | `94.85% <ø> (ø)` | |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/21797/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.19% <ø> (ø)` | |
| ... and [6 more](https://codecov.io/gh/pandas-dev/pandas/pull/21797/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21797?src=pr&el=continue).
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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21797?src=pr&el=footer). Last update [9e1f6fd...376617d](https://codecov.io/gh/pandas-dev/pandas/pull/21797?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jorisvandenbossche look ok? @jreback .. I modified the files.. but noticed you already approved the changes.. do you want me to modify the PR or leave it as is? @alphaCTzo7G is ok for now. Heres the patch in case you want to apply it in this or in a different PR: https://github.com/alphaCTzo7G/pandas/commit/c27b5f45ee4be493bb76995d319a073026f6acf5 > Heres the patch in case you want to apply it in this or in a different PR: alphaCTzo7G/pandas@c27b5f4

Can you add that commit here to this PR? (pushing to the branch should do that) Done... @alphaCTzo7G Thanks a lot !