Add stubs for ujson

[Michael0x2a]

This pull request adds stubs for ujson. Note that the interface for ujson is a bit more restrictive then the interface for the json module in the standard library.

[gvanrossum]

Have you checked with the developers of ujson whether they are okay with including these stubs in typeshed? Our policy for third_party packages requires checking this. You can probably just ask them in their tracker and once they respond, link back to their tracker issue here.

[gvanrossum]

PS. Would be nice if we had a bot that automatically asked that whenever someone submits stubs for a new package in third_party.

[Michael0x2a]

I asked them just now, and they were ok with it: ultrajson/ultrajson#233

[timabbott]

@Michael0x2a how confident are you that the ujson methods take a str (as opposed to e.g. an AnyStr)? I haven't looked too closely, but based on ultrajson/ultrajson#11, it seems current ujson is intended to return a unicode if you pass it a unicode, I think?

[timabbott]

(For context, I'm getting errors trying to use this with the Zulip project, which has annotations assuming that e.g. ujson.loads can be passed a Text object. It's possible those annotations are wrong, but I'd be a bit surprised...)

[gvanrossum]

Can't you just try this in the REPL? Should take 1 minute if you have ujson installed and will tell you the truth.

[Michael0x2a]

Hmm, you might be right -- in retrospect, I'm not sure if I tested my stubs very thoroughly on Python 2.

I did some quick testing, and it seems like the loads functions most likely can take in strings of type Union[Text, bytes]. The dumps functions seem a bit more complicated -- they seem to return str in both Python 2 and Python 3 (which means they're really returning bytes in Python 2 and Text in Python 3?).

But perhaps I'm wrong about this again.

[timabbott]

Yeah, I just tested as well and indeed loads at least can take Text and bytes.

[timabbott]

Opened #540 to fix this issue. Thanks @Michael0x2a for also investigating this :)