CLN: Cleanup WorldBank reader

[sinhrks]

Closes #120 to remove urlopen.

Related #119, changed some default arg using list to None (and set them in the method).

CC @femtotrader

[femtotrader]

You might pass session parameter to each functions which should download data in order to also provide cache mechanism to WorldBank data reader. (CC @davidastephens )

[femtotrader]

Sorry. In fact, there is now a class WorldBankReader which is a great improvement.

but you might to also pass a session parameter to download, get_countries, get_indicators, search functions and send this session parameter to WorldBankReader.__init__

[femtotrader]

An other improvement might be about errors parameter.

We shouldn't use string but Enum (enum34 for Python 2) as it wil allow tab completion.

[femtotrader]

A last idea (about methods of WorldBankReader)...

get_countries and get_indicators might be properties named countries and indicators as there is no parameter (except self) for these 2 WorldBankReader methods.

[femtotrader]

I thought that it was the last idea... but sorry I also noticed that there is a per_page parameter in urls.

We might support chunks and use page parameter

try
http://api.worldbank.org/countries/?per_page=1000000&format=json&page=1

and

http://api.worldbank.org/countries/?per_page=100&format=json&page=1
http://api.worldbank.org/countries/?per_page=100&format=json&page=2

but this is probably out of the scope of this PR and an issue should be opened for this.

[sinhrks]

@femtotrader Thanks for the comments. I've updated the PR as below. I intend this PR to cover existing functionality, and others should be handled separately.

• Add session to WB's get_xxx funcs: Done. As other kw such as retry may be useful, passed all kwds to WorldBankReader class (same as other get_data_xxx funcs)
• Change get_indicators and get_countries to property: Don't do. I don't think the names are very understandable for users which is different from plain get_xxx functions.
• Change errors to enum: Don't do in this PR. Because pandas doesn't use enum. Pls prepare a PR separately.
• Add page param: Don't do in this PR.

[femtotrader]

Thanks a lot for you work. You are right! Other improvements should be done in an other PR.

[femtotrader]

Sorry @sinhrks I think that there is a mistake with

return WorldBankReader().get_countries(**kwargs)

it should be

return WorldBankReader(**kwargs).get_countries()

[sinhrks]

@femtotrader Thanks! Fixed and added tests.