field/key remapping

json_field_remapping.py

from dataclasses import dataclass
from .remappers import Alias, remapper  # see module `remappers.py` below


@dataclass
class DiveSpot(metaclass=remapper):
    id: str = Alias('_id')
    name: str = Alias('divespot')

    # stub to satisfy external linters and type checkers
    def __init__(self, **kwargs): ...


ds = DiveSpot()
print(ds)  # DiveSpot(id=None, name=None)

data = {'_id': '5719fdf6edf5136d37aaf562', 'divespot': 'The Tugs', 'divesite': 'Fathom Five National Park', 'region': 'Ontario', 'country': 'Canada'}

ds = DiveSpot(**data)
print(ds)  # DiveSpot(id='5719fdf6edf5136d37aaf562', name='The Tugs')

ds = DiveSpot(id='test', name='my name')
print(ds)  # DiveSpot(id='test', name='my name')

remappers.py

from dataclasses import _create_fn


def remapper(name, bases, cls_dict):

    def __init__(self, **kwargs):
        cls = self.__class__

        # create a sentinel "missing" type, as `dataclasses` also does
        class _MISSING_TYPE:
            ...

        lines = ['_get = kwargs.get']
        lines.extend(f'r = _get("{other_key}", _MISSING); '
                     f'self.{attr} = _get("{attr}") if r is _MISSING else r'
                     for other_key, attr in cls.__remapping__.items())

        init_fn = cls.__init__ = _create_fn('__init__', ('self', '**kwargs'), lines,
                                            locals={'_MISSING': _MISSING_TYPE()})
        return init_fn(self, **kwargs)

    cls_dict.update(
        __init__=__init__,
        __remapping__={},
    )

    cls = type(name, bases, cls_dict)
    return cls


class Alias:

    __slots__ = ('_other_name', )

    def __init__(self, other_name: str):
        self._other_name = other_name

    def __set_name__(self, owner, name):
        owner.__remapping__[self._other_name] = name