DOC: require returns section in validation script
Are there cases where do not want a "Returns" section? 

cc @datapythonista 


# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19994?src=pr&el=h1) Report
> Merging [#19994](https://codecov.io/gh/pandas-dev/pandas/pull/19994?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/024d8b447ec9933373d28ab29ec1c198993bef61?src=pr&el=desc) will **decrease** coverage by `0.03%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19994/graphs/tree.svg?width=650&height=150&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/19994?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19994      +/-   ##
==========================================
- Coverage   91.72%   91.68%   -0.04%     
==========================================
  Files         150      150              
  Lines       49112    49065      -47     
==========================================
- Hits        45047    44986      -61     
- Misses       4065     4079      +14
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.06% <ø> (-0.04%)` | :arrow_down: |
| #single | `41.88% <ø> (+0.01%)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19994?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/tseries/plotting.py](https://codecov.io/gh/pandas-dev/pandas/pull/19994/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvcGxvdHRpbmcucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/core/missing.py](https://codecov.io/gh/pandas-dev/pandas/pull/19994/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvbWlzc2luZy5weQ==) | `85.9% <0%> (-5.75%)` | :arrow_down: |
| [pandas/plotting/\_timeseries.py](https://codecov.io/gh/pandas-dev/pandas/pull/19994/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL190aW1lc2VyaWVzLnB5) | `60.82% <0%> (-4.49%)` | :arrow_down: |
| [pandas/io/packers.py](https://codecov.io/gh/pandas-dev/pandas/pull/19994/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhY2tlcnMucHk=) | `87.31% <0%> (-0.89%)` | :arrow_down: |
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/19994/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `96.66% <0%> (ø)` | :arrow_up: |
| [pandas/plotting/\_core.py](https://codecov.io/gh/pandas-dev/pandas/pull/19994/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb3JlLnB5) | `82.23% <0%> (ø)` | :arrow_up: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/19994/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.66% <0%> (ø)` | :arrow_up: |
| [pandas/core/window.py](https://codecov.io/gh/pandas-dev/pandas/pull/19994/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvd2luZG93LnB5) | `96.32% <0%> (ø)` | :arrow_up: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/19994/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `95.88% <0%> (+0.04%)` | :arrow_up: |
| [pandas/core/indexes/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/19994/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZWxpa2UucHk=) | `96.83% <0%> (+0.12%)` | :arrow_up: |
| ... and [4 more](https://codecov.io/gh/pandas-dev/pandas/pull/19994/diff?src=pr&el=tree-more) | |

------

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 I think the only cases are when the function/method does not return anything (I would about a return None), when a class it's being documented, or when the function yields its value.

If I'm not wrong, it should be easy in Python to detect whether it's a class or a generator yielding the values. But not sure if there is an easy way to detect that a function doean't have a return, or all returns return None lgtm. > I think the only cases are when the function/method does not return anything (I would about a return None), when a class it's being documented, or when the function yields its value.

I don't think we have many functions/methods in pandas that do not return anything (except for the inplace ones, but that is always an option)