remove docs from packages
- ~closes #xxxx~
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

#30741 discusses removing documentation and tests from package distributions. This is valuable because it makes `pandas` easier to use in storage-sensitive environments such as AWS Lambda (https://github.com/pandas-dev/pandas/issues/30741#issuecomment-638158062, https://github.com/pandas-dev/pandas/issues/30741#issuecomment-752751976).

This PR does not close that issue, but it's a first step. This proposes removing the content of `doc/`  from package distributions. This PR trims about 1MB (compressed) and 6MB (uncompressed) out of the `sdist` package.

|                                        |  `master`  | this PR   |
|:-----------------------:|:----------:|:--------:|
| sdist (compressed)       |     5.7M      |  4.5M     |
| sdist (uncompressed)   |     25M       |  19M      |

<details><summary>how I checked these sizes</summary>

```shell
rm -rf pandas.egg-info
rm -rf dist/
rm -rf __pycache__

echo ""
echo "building source distribution"
echo ""
python setup.py sdist > /dev/null
cp pandas.egg-info/SOURCES.txt ~/PANDAS-SOURCES.txt
pushd dist/
    echo ""
    echo "sdist compressed size"
    echo ""
    du -a -h .
    tar -xf pandas*.tar.gz
    rm pandas*.tar.gz
    ls .
    echo ""
    echo "sdist uncompressed size"
    echo ""
    du -sh .
popd
```

</details>

To confirm that the documentation files were removed correctly by these changes, I ran the following

```shell
python setup.py sdist
cat pandas.egg-info/SOURCES.txt | grep -E "^doc"
```

Thanks for your time and consideration.
@jameslamb can you add a note in 1.3. Other API changes section (make a separete entry, call it Build)
 cc @simonjayhawkins if you can have a test on this to make sure build looks ok. @jameslamb we might also want to have that check in https://github.com/pandas-dev/pandas-release, if you can make an issue / PR there as well. > @jameslamb can you add a note in 1.3. Other API changes section (make a separete entry, call it Build)

sure! Added in https://github.com/pandas-dev/pandas/pull/38846/commits/3aee9b9555677b03e4a2b30469d5aa34aa2b0070, let me know if that wasn't what you meant. > @jameslamb we might also want to have that check in https://github.com/pandas-dev/pandas-release, if you can make an issue / PR there as well.

Sorry, I don't understand what you'd like me to add to `pandas-release`. Could you elaborate? > > @jameslamb we might also want to have that check in https://github.com/pandas-dev/pandas-release, if you can make an issue / PR there as well.
> 
> Sorry, I don't understand what you'd like me to add to `pandas-release`. Could you elaborate?

an issue / PR that makes a test like you did above. that repo actually builds the releases and should check that no docs are present via a test. ooooo I see! Yep ok, I can do that Ok I've attempted a `pandas-release` PR at https://github.com/pandas-dev/pandas-release/pull/35. I've also updated this PR to the latest `master`. this looks fine. @simonjayhawkins ok? Rather than outright removing would we consider a `no-doc` specification as outlined in [PEP 508](https://www.python.org/dev/peps/pep-0508/#id17) ? By default I think including documentation is a good thing > Rather than outright removing would we consider a `no-doc` specification as outlined in [PEP 508](https://www.python.org/dev/peps/pep-0508/#id17) ? By default I think including documentation is a good thing

could you provide specific reasons why you think it's valuable to include documentation like [these Powerpoint files](https://github.com/pandas-dev/pandas/tree/bdcefdd047d6eaacb1f12a0b2f9daedc1b3cb9f1/doc/cheatsheet) in package distributions?

There was already substantial discussion on #30741 about the **disadvantages** of doing that (for example, https://github.com/pandas-dev/pandas/issues/30741#issuecomment-638158062 and https://github.com/pandas-dev/pandas/issues/30741#issuecomment-752751976), and @jreback agreed with the proposal in this PR. Sure - if you are ever without internet and try to develop anything with pandas having the documentation available locally is invaluable. I also think it is relatively standard to include. At least other libraries like numpy and scikit-learn keep their doc folders in the sdist.

The powerpoint is a little different and I think fine to exclude regardless, but I do think PEP 508 would be a better solution for all Thanks for clarifying. In my opinion, that use case is one that describes a very small minority of all the users (machine and human) that `pip install pandas`.

Because I believe that use case describes a small minority of all users, I think that if you wanted to provide support for it, it would be more appropriate to make that the optional thing you have to opt in to (e.g. `pip install pandas[include-docs]`).

I think the possible benefit of removing around 1MB of data transfer and around 6MB of uncompressed size on disk per install for users who have slow internet connections or who are storage-conscious (like AWS Lambda users) far outweighs the downside of not supporting by default the use case where someone has no internet access and wants to read the long-form `pandas` docs (they can always `help()` on any object in the library to get its dosctring).

One more point I'd like to make in favor of this change. A conservative reading of the last few months of data available at  https://pypistats.org/packages/pandas suggests that `pandas` is installed from PyPi 500,000 times a day. That means that the changes in this PR might cut 500GB of daily data transfer from PyPi, without breaking anyone's existing code. I'd like you and other maintainers who comment on this to consider whether it is worth forgoing that benefit and the others mentioned above and in #30741 to preserve the behavior "if you've installed pandas successfully, all of the long-form documentation is available to you locally". Is there some additional information I could provide or changes reviewers would like me to make?

I've been merging the latest `master` into this PR every few days for the last few months, and I'd be happy to do whatever I can to move this to resolution (even if that resolution is maintainers deciding to reject this change).

Thanks. I think the pdf / ppts are fine to exclude regardless, but for more general documentation I would still prefer to go the PEP 508 route. This has an additional advantage that you can provide further optimizations like the `-OO` switch if you are really trying to minimize package size I'm fine with either this or @WillAyd's method.  If we go with this, the whatsnew should have a "to pip install with the documents do XYZ" yeah let's start with excluding the pdfs / ppts and see how that goes. @jameslamb if you'd update.  Alright. Updated in https://github.com/pandas-dev/pandas/pull/38846/commits/648187ae841da4244a2d096d118432a976d75e3d.

After that change, here's an updated version of the table from the original description. 

|                                        |  `master`  | this PR   |
|:-----------------------:|:----------:|:--------:|
| sdist (compressed)       |     5.4M      |  4.6M     |
| sdist (uncompressed)   |     40M       |  39M      |
 thanks @jameslamb 
