Enhancement Add max_level param to json_normalize
- [x] closes #23843
- [x] closes #23861
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry


# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26876?src=pr&el=h1) Report
> Merging [#26876](https://codecov.io/gh/pandas-dev/pandas/pull/26876?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/430f0fd04646a0ab44ccbfbad706dfe22e9fabfe?src=pr&el=desc) will **decrease** coverage by `50.78%`.
> The diff coverage is `20%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26876/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26876?src=pr&el=tree)

```diff
@@             Coverage Diff             @@
##           master   #26876       +/-   ##
===========================================
- Coverage   91.88%   41.09%   -50.79%     
===========================================
  Files         179      179               
  Lines       50696    50697        +1     
===========================================
- Hits        46581    20836    -25745     
- Misses       4115    29861    +25746
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `?` | |
| #single | `41.09% <20%> (-0.08%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26876?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/json/normalize.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2pzb24vbm9ybWFsaXplLnB5) | `8.08% <20%> (-88.86%)` | :arrow_down: |
| [pandas/io/formats/latex.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvbGF0ZXgucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/plotting/\_matplotlib/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19tYXRwbG90bGliL19faW5pdF9fLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/gcs.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2djcy5weQ==) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/sas/sas\_constants.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfY29uc3RhbnRzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/core/groupby/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9jYXRlZ29yaWNhbC5weQ==) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/plotting.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvcGxvdHRpbmcucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/s3.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3MzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/formats/html.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvaHRtbC5weQ==) | `0% <0%> (-99.37%)` | :arrow_down: |
| [pandas/io/sas/sas7bdat.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXM3YmRhdC5weQ==) | `0% <0%> (-91.16%)` | :arrow_down: |
| ... and [133 more](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26876?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/26876?src=pr&el=footer). Last update [430f0fd...aed2db5](https://codecov.io/gh/pandas-dev/pandas/pull/26876?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26876?src=pr&el=h1) Report
> Merging [#26876](https://codecov.io/gh/pandas-dev/pandas/pull/26876?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/e9555159afd8caabc88b45ca6c06a16efe2f6afc?src=pr&el=desc) will **decrease** coverage by `1.4%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26876/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26876?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26876      +/-   ##
==========================================
- Coverage   92.04%   90.64%   -1.41%     
==========================================
  Files         180      180              
  Lines       50714    50756      +42     
==========================================
- Hits        46679    46007     -672     
- Misses       4035     4749     +714
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.64% <100%> (-0.04%)` | :arrow_down: |
| #single | `?` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26876?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/json/normalize.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2pzb24vbm9ybWFsaXplLnB5) | `97% <100%> (+0.06%)` | :arrow_up: |
| [pandas/core/computation/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vcHl0YWJsZXMucHk=) | `62.5% <0%> (-27.75%)` | :arrow_down: |
| [pandas/io/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3B5dGFibGVzLnB5) | `64.86% <0%> (-25.44%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `88.88% <0%> (-11.12%)` | :arrow_down: |
| [pandas/core/computation/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vY29tbW9uLnB5) | `84.21% <0%> (-5.27%)` | :arrow_down: |
| [pandas/core/computation/expr.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vZXhwci5weQ==) | `94.78% <0%> (-3.03%)` | :arrow_down: |
| [pandas/io/clipboard/clipboards.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2NsaXBib2FyZC9jbGlwYm9hcmRzLnB5) | `31.88% <0%> (-2.9%)` | :arrow_down: |
| [pandas/io/formats/printing.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvcHJpbnRpbmcucHk=) | `85.78% <0%> (-0.95%)` | :arrow_down: |
| [pandas/core/internals/managers.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL21hbmFnZXJzLnB5) | `96.09% <0%> (-0.77%)` | :arrow_down: |
| [pandas/core/internals/blocks.py](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2Jsb2Nrcy5weQ==) | `94.61% <0%> (-0.53%)` | :arrow_down: |
| ... and [7 more](https://codecov.io/gh/pandas-dev/pandas/pull/26876/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26876?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/26876?src=pr&el=footer). Last update [e955515...676c7f1](https://codecov.io/gh/pandas-dev/pandas/pull/26876?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Hello @bhavaniravi! 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 2019-06-29 15:25:42 UTC what is the relation of #23861 to this PR? this is just *max_level* right? if so is there a reason to keep the #23861 open? also can you add a small example in the io/json doc section & a small sub-section in the whatsnew showcasing this (use one of the test cases that you have as they are pretty short). list both issues that you are closing. code & tests look good, can you add a note in whatsnew (other enhancements); also consider if we should update the docs in io.rst (adding an example using max_level) > code & tests look good, can you add a note in whatsnew (other enhancements); also consider if we should update the docs in io.rst (adding an example using max_level)

@jreback I assumed docstrings would generate the docs in pandas/doc folder, now I am anticipating that's not right. So should we manually add it with the ipython constructs? > > code & tests look good, can you add a note in whatsnew (other enhancements); also consider if we should update the docs in io.rst (adding an example using max_level)
> 
> @jreback I assumed docstrings would generate the docs in pandas/doc folder, now I am anticipating that's not right. So should we manually add it with the ipython constructs?

I am requesting an entry in doc/source/whatsnew/v0.25.0.txt & any updates in io.rst that are needed Looks like a remaining lint error but otherwise lgtm > lgtm - thanks for sticking through review

My pleasure. I learned alot along the way. Thank you for being so patient with me.  @jreback @WillAyd What next? I am ready to open the next PR for `ignore_keys` once this is merged Thanks @bhavaniravi!