exttr 2019.2.2

Integrating extra metadata into attr.ib()

Integrating extra metadata into attr.ib()

Example

With a little luck a better example will be provided later but for now, here’s something.

A dev in #python was interested in having click build them attrs-defined configuration objects. Here’s a basic solution for that with the click options being defined on the attrs class attributes via a custom exttr keyword argument click=.

import collections
import sys

import attr
import click
import exttr


exttr.register_keywords(
    exttr.Keyword(name='click'),
)


@attr.s
class Configuration:
    foo = exttr.ib(click=click.option('--red'))


def main(configuration):
    print(configuration)

def clicked_fields(cls):
    fields = collections.OrderedDict()

    for field in attr.fields(cls):
        decorator = exttr.get(cls, field.name, 'click')

        if decorator is None:
            continue

        fields[field.name] = decorator

    return fields


def build_click(f, cls, command_or_group):
    fields = clicked_fields(cls)

    def cli(*args, **kwargs):
        configuration = cls(*args, **kwargs)

        return f(configuration)

    for name, decorator in reversed(fields.items()):
        before = getattr(cli, '__click_params__', [])

        cli = decorator(cli)

        after = getattr(cli, '__click_params__', [])
        new = after[len(before):]

        if len(new) == 1:
            new, = new
            new.name = name

    return command_or_group(cli)


click_main = build_click(
    f=main,
    cls=Configuration,
    command_or_group=click.command(),
)


sys.argv[1:] = ['--red', 'burgundy']
try:
    click_main()
except SystemExit:
    pass

Output:

Configuration(foo='burgundy')