Avoid code deduplication with attrs

[guyzmo]

The code relies a lot on a common super-verbose pattern:

class GogsFoobar:
    def __init__(self, param):
        self._param = param

    @staticmethod
    def from_json(self, parsed_json):
        param = parsed_json.get(param, 42)
        return GogsFoobar(param=param)

    @property
    def param(self):
        return self._param

you end up writing 9 times param, for each attribute you add. I love python, and things being explicit better than implicit, but we're light years away from DRY here. This is being…

I suggest instead to use some tricks like, the attrs module:

import attr

@attr.s(frozen=True)
class GogsFoobar:
    foobar = attr.ib(default=42)

    @staticmethod
    def from_json(self, parsed_json):
        param = parsed_json.get(param, 42)
        return GogsFoobar(param=param)

it's now down to 4.

But we can make it totally DRY, the following way:

import attr

@attr.s
class GogsEntity:
    json = attr.ib()
    @classmethod
    def from_json(cls, parsed_json):
        # with introspection, get arguments of the constructor
        params = attr.fields(cls)
        args = []
        kwargs = {}
        for param in params:
            # if not a keyword argument
            if param.name == attr._make._Nothing:
                args.append(json_get(parsed_json, param.name))
            # if it's a keyword argument
            else:
                kwargs[param.name] = parsed_json.get(param.name, None)
        del kwargs['json']
        instance = cls(*args, json=parsed_json, **kwargs)
        return instance

@attr.s(frozen=True)
class GogsFoobar(GogsEntity):
    foo = attr.ib()
    foobar = attr.ib(default=42)

x = GogsFoobar.from_json(dict(foo=1, foobar=2))

print(x.foo, x.foobar, x.json)

and now you only write the attribute once. But I agree, it's using some creepy dirty internal automagic from python. At the cost of making it uglier in one place, you make it DRY everywhere else, with the same strong type checkings you enforce currently.

[guyzmo]

(if you checked you email first, note that I updated the issue to make the code better and working ☺)

[ethantkoenig]

Resolved by d3db08e