Move json_normalize to pd namespace
- Added a whatsnew entry
- Imported pandas.io.json.json_normalize in __init__.py

- [x] closes #27586 
- [x] whatsnew entry

cc: @WillAyd 
Makes sense for the move. @TomAugspurger do you know how we've messaged things like this to users in the past to not import from pandas.io.json anymore? I don't recall on messaging. Probably something "Accessing json_normalize from pandas.io has been deprecated and will be removed in a future version. Uses pandas.json_normalize instead."

But we'll need to make a `pandas.io._json_normalize` that has the implementation, and `pandas.io.json_normalize` will warn then call that. `pandas/__init__.py` will import `io._json_normalize as json_normalize`. Thanks for review @jreback, please allow me to get back on this by the end of the weekend if that’s ok. I’ll also incorporate @TomAugspurger’s comment on deprecation as well. Thanks! No rush, we’re still a ways out from 1.0. 

> On Jul 26, 2019, at 17:37, Vishwak Srinivasan <notifications@github.com> wrote:
> 
> Thanks for review @jreback, please allow me to get back on this by the end of the weekend if that’s ok. I’ll also incorporate @TomAugspurger’s comment on deprecation as well.
> 
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 Hello @vishwakftw! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:











There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2019-12-18 19:02:46 UTC Looks like the docs need to be updated: https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=15186

The line numbers may be a bit off, but hopefully close enough. Can you update `doc/source/reference/io.rst` so that the reference docs for `json_normalize` are for the top-level?

It seems that `build_table_scheme` also is exposed. Would you be willing to do a similar change for it? Either here or as a followup. > Can you update doc/source/reference/io.rst so that the reference docs for json_normalize are for the top-level?

Yes, will do that.

> It seems that build_table_scheme also is exposed. Would you be willing to do a similar change for it? Either here or as a followup.

Would you like me to expose `build_table_schema` in the pd namespace? Possibly. I didn't closely follow the issue discussing json_nomalize, but
we should be consistent. @jreback thoughts?

On Mon, Jul 29, 2019 at 9:54 AM Vishwak Srinivasan <notifications@github.com>
wrote:

> Can you update doc/source/reference/io.rst so that the reference docs for
> json_normalize are for the top-level?
>
> Yes, will do that.
>
> It seems that build_table_scheme also is exposed. Would you be willing to
> do a similar change for it? Either here or as a followup.
>
> Would you like me to expose build_table_schema in the pd namespace?
>
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 I also just commented on the issue about `build_table_schema` (https://github.com/pandas-dev/pandas/issues/27586), but I am not sure that that warrants a top-level function. `build_table_schema` doesn't deserve a top level function as it's not generally useful for end users (it's one part of actually writing out in the table format) 

It's unfortunate that `json_normalize` leaked publicly the way it is now but it certainly has usage and enhancement requests coming in for it, hence this PR I wouldn't say "leaked publicly" though, right? That's the intentional,
documented location for it.

On Wed, Jul 31, 2019 at 4:06 PM William Ayd <notifications@github.com>
wrote:

> build_table_schema doesn't deserve a top level function as it's not
> generally useful for end users (it's one part of actually writing out in
> the table format)
>
> It's unfortunate that json_normalize leaked publicly the way it is now
> but it certainly has usage and enhancement requests coming in for it, hence
> this PR
>
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>
 Can’t speak to the entire history of intention but looks like was added alongside read_json in #10301 but never moved to the top level whenever read_json was

In any case I don’t think whatever we do with this function needs to dictate what happens for build_table_schema

> On Jul 31, 2019, at 2:09 PM, Tom Augspurger <notifications@github.com> wrote:
> 
> I wouldn't say "leaked publicly" though, right? That's the intentional,
> documented location for it.
> 
> On Wed, Jul 31, 2019 at 4:06 PM William Ayd <notifications@github.com>
> wrote:
> 
> > build_table_schema doesn't deserve a top level function as it's not
> > generally useful for end users (it's one part of actually writing out in
> > the table format)
> >
> > It's unfortunate that json_normalize leaked publicly the way it is now
> > but it certainly has usage and enhancement requests coming in for it, hence
> > this PR
> >
> > —
> > You are receiving this because you were mentioned.
> > Reply to this email directly, view it on GitHub
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> > or mute the thread
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> >
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> 

 @vishwakftw can you check doc failure and merge master? @WillAyd I can't seem to understand where the doc is failing. Could you help? Hmm I guess the old build logs got cleared. Just restarted it so error should show again in say 20 minutes  @WillAyd The requested changes have been applied. Sorry about the delay in getting to them. @WillAyd extremely sorry for not getting to the comments earlier, I've addressed your most recent comments. @vishwakftw is this still active? Can you merge master and repush? @WillAyd I was unsure about how to deprecate on import, and was wondering if you had an idea (https://github.com/pandas-dev/pandas/pull/27615/#discussion_r330086223). not sure; this might be OK as is if you can get CI to pass will take another look I'm not sure if the CI failures are relevant. Looks like you need to run black on the changes to pass CI

I’ll take a look at the rest this weekend @vishwakftw can you fix conflicts and ping on green @WillAyd Sure, I've rebased and will ping you once green. @WillAyd There is one failure, I'm not sure if it is related:
```
=================================== FAILURES ===================================

______________________________ test_scikit_learn _______________________________

[gw1] linux -- Python 3.6.9 /home/travis/miniconda3/envs/pandas-dev/bin/python

df =    A

0  1

1  2

2  3

    @pytest.mark.filterwarnings("ignore:can't:ImportWarning")

    def test_scikit_learn(df):

    

>       sklearn = import_module("sklearn")  # noqa

pandas/tests/test_downstream.py:72: 

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

pandas/tests/test_downstream.py:20: in import_module

    return importlib.import_module(name)

../../../miniconda3/envs/pandas-dev/lib/python3.6/importlib/__init__.py:126: in import_module

    return _bootstrap._gcd_import(name[level:], package, level)

<frozen importlib._bootstrap>:994: in _gcd_import

    ???

<frozen importlib._bootstrap>:971: in _find_and_load

    ???

<frozen importlib._bootstrap>:955: in _find_and_load_unlocked

    ???

<frozen importlib._bootstrap>:665: in _load_unlocked

    ???

<frozen importlib._bootstrap_external>:678: in exec_module

    ???

<frozen importlib._bootstrap>:219: in _call_with_frames_removed

    ???

../../../miniconda3/envs/pandas-dev/lib/python3.6/site-packages/sklearn/__init__.py:75: in <module>

    from .utils._show_versions import show_versions

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

    """

    # License: BSD 3 clause

    

    import platform

    import sys

    import importlib

    

>   from ._openmp_helpers import _openmp_parallelism_enabled

E   ImportError: dlopen: cannot load any more object with static TLS

../../../miniconda3/envs/pandas-dev/lib/python3.6/site-packages/sklearn/utils/_show_versions.py:12: ImportError
``` Should have been resolved with changes to CI yesterday. Looks like another merge conflict - if you clean up and repush should be green now I think @WillAyd the CI is green now Great job with this @vishwakftw ! Thank you @WillAyd. Apologies for the delay in getting this merged.