TAJO-1332 Implement Python Client for Tajo

[charsyam]

This is implement of python tajo rest client.

[charsyam]

This is a PR just for discuss more.
we should discuss about testing and distribution and directory of this kind of clients.

I just put the python client into contrib/tajo-python
but it should be discussed for right position.

[hyunsik]

Great work! I think that contrib seems to be a right position. I'll review it soon.

[jihoonson]

Nice work! On the proper location, I agree with you guys.

[hyunsik]

I'm sorry for late review. The protocol between client and TajoMaster has been rapidly changed for better error propagation (https://issues.apache.org/jira/browse/TAJO-1625). This changes will actually affect REST API specification. I thought that this patch is conflict to the on-going error propagation work.

The solution is that we have to improve REST API to reflect the error propagation before we can continue this Python client. I think that REST API improvements is trivial. We can put this python client into the next release.

[blrunner]

Hi @charsyam

Thank you for your contribution.

Python has an API to make it easy to move from one SQL-based DB to another called DB-API. Each DB may have multiple different modules available for it. And if python users use it, they would easy integrate python applications with ORM. It's documented in https://www.python.org/dev/peps/pep-0249.

If you implement it, Tajo python client would be better. Could you consider my suggestion?

[eminency]

Hi, @charsyam

May I take this on to continue?

[charsyam]

@eminency Thanks for your suggestion.
but, If you excuse. I will finish it ASAP
Thanks.