### What is this PR for?
This PR is the first of two major steps needed to improve matplotlib integration in Zeppelin (ZEPPELIN-1344). The latter, which is a plotting backend with fully interactive tools enabled, will be done afterwards in a separate PR. This PR specifically for automatically displaying output from calls to matplotlib plotting functions inline with each paragraph. Thanks to the addition of post-execute hooks (ZEPPELIN-1423), there is no need to call any `show()` function to display an inline plot, just like in Jupyter.
### What type of PR is it?
Improvement
### Todos
The main code has been written and anyone who reads this is encouraged to test it, but there are a few minor todos:
- [x] - Add unit tests
- [x] - Add documentation
- [x] - Add screenshot showing iterative plotting with angular mode
### What is the Jira issue?
[ZEPPELIN-1345](https://issues.apache.org/jira/browse/ZEPPELIN-1345)
### How should this be tested?
In a pyspark or python paragraph, enter and run
``` python
import matplotlib.pyplot as plt
plt.plot([1, 2, 3])
```
The plot should be displayed automatically without calling any `show()` function whatsoever. A special method called `configure_mpl()` can also be used to modify the inline plotting behavior. For example,
``` python
z.configure_mpl(close=False, angular=True)
plt.plot([1, 2, 3])
```
allows for iterative updates to the plot provided you have PY4J installed for your python installation (which of course is always the case if you use pypsark). To clarify, this feature only currently works with pyspark (not python as there are no `angularBind()` and `angularUnbind()` methods yet). Doing something like:
```
plt.plot([3, 2, 1])
```
will update the plot that was generated by the previous paragraph by leveraging Zeppelin's Angular Display System. However, by setting `close=False`, matplotlib will no longer automatically close figures so it is now up to the user to explicitly close each figure instance they create. There's quite a bit more options for `z.configure_mpl()`, but I will save that discussion for the documentation.
### Screenshots (if appropriate)
### Questions:
- Does the licenses files need update? No
- Is there breaking changes for older versions? No
- Does this needs documentation? Yes
Author: Alex Goodman <agoodm@users.noreply.github.com>
Closes#1534 from agoodm/ZEPPELIN-1345 and squashes the following commits:
9ef6ff7 [Alex Goodman] Move mpl backend files to /interpreter
24f89c6 [Alex Goodman] Catch potential NullPointerExceptions from hook registry
bdb584e [Alex Goodman] Make sure expressions are printed when no plots are shown
22b6fe4 [Alex Goodman] Remove unused variable
d3d1aa0 [Alex Goodman] Fix CI test failure
c90d204 [Alex Goodman] Update spark.md
bcf0bf3 [Alex Goodman] Update python.md for new matplotlib integration
c9b65a5 [Alex Goodman] Add iterative plotting example image
8029a05 [Alex Goodman] Update python/README.md
f2d9e86 [Alex Goodman] Exclude tests are excluded in python/pom.xml
86b1c90 [Alex Goodman] Fix tutorial notebook not loading
c37b00f [Alex Goodman] Fix legend in tutorial notebook
a321d79 [Alex Goodman] Update python.md
82350e3 [Alex Goodman] Update matplotlib tutorial notebook
9792f97 [Alex Goodman] Add unit tests
8b9b973 [Alex Goodman] Fix NullPointerExceptions in unit tests
82135ad [Alex Goodman] Removed unused variable
f9c9498 [Alex Goodman] Added support for Angular Display System
edf750a [Alex Goodman] Add new matplotlib backend for python/pyspark interpreters
### What is this PR for?
Add new interpreter to Python group: `%python.sql` for SQL over DataFrame support
### What type of PR is it?
Improvement
### TODOs
* [x] add new interpreter `%python.sql`
* [x] add test
* [x] make Python-dependant tests, excluded from CI
* PythonInterpreterWithPythonInstalledTest
* PythonPandasSqlInterpreterTest
* run manually by `mvn -Dpython.test.exclude='' test -pl python -am`
* [x] add docs `%python.sql`
* [x] make `%python.sql` fail gracefully in case there is no Pandas or PandaSQL installed
* [x] after #747 is merged - rebase and remove `-Dpython.test.exclude=''` from both profiles
### What is the Jira issue?
[ZEPPELIN-1115](https://issues.apache.org/jira/browse/ZEPPELIN-1115)
### How should this be tested?
`mvn -Dpython.test.exclude='' test -pl python -am` should pass or manually run
- Given the DataFrame i.e
```
%python
import pandas as pd
rates = pd.read_csv("bank.csv", sep=";")
```
- SQL query it like
```
%python.sql
SELECT * FROM rates LIMIT 10
```
### Screenshots (if appropriate)
### Questions:
* Does the licenses files need update? No, no dependencies were included in source or binary release
* Is there breaking changes for older versions? No
* Does this needs documentation? Yes
Author: Alexander Bezzubov <bzz@apache.org>
Closes#1164 from bzz/ZEPPELIN-1115/python/add-sql-for-dataframes and squashes the following commits:
0f2f852 [Alexander Bezzubov] Fail SQL gracefully if no python dependencies installed
aca2bdf [Alexander Bezzubov] Fix typos in docs ⚡158ba6a [Alexander Bezzubov] Remove third-party dependant test from CI
5fe46fc [Alexander Bezzubov] Update Python Matplotlib notebook example
72884c8 [Alexander Bezzubov] Add docs for %python.sql feature
e931dc4 [Alexander Bezzubov] Make test for PythonPandasSqlInterpreter usable
76bbb44 [Alexander Bezzubov] Complete implementation of the PythonPandasSqlInterpreter
f6ca1eb [Alexander Bezzubov] Add %python.sql to interpreter menue
11ba490 [Alexander Bezzubov] Add draft implementation of %python.sql for DataFrames
### What is this PR for?
This is first step improving current Python interpreter implementation.
It has just a cleanup, style and docs improvements.
### What type of PR is it?
Improvement
### Questions:
* Does the licenses files need update? No
* Is there breaking changes for older versions? No
* Does this needs documentation? No
Author: Alexander Bezzubov <bzz@apache.org>
Closes#1021 from bzz/improve/python and squashes the following commits:
3cafa22 [Alexander Bezzubov] Python: make interpreter logs less verbose
744f7d2 [Alexander Bezzubov] Python: move technical details from doc to README.md
0f74e5d [Alexander Bezzubov] Python: return first running job
08c2bb4 [Alexander Bezzubov] Python: upd Java code to conform project conventions
e84cd5c [Alexander Bezzubov] Python: normalize newlines in python
58efcc9 [Alexander Bezzubov] Python: normalize newlines in Java
