extension to convert dataclasses with cattrs.

dataclass_converter.py

import dataclasses
from .converters import Converter


def _is_dataclasses_class(obj):
    return dataclasses.is_dataclass(obj)


class DataclassesConverter(Converter):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.register_unstructure_hook_func(
            _is_dataclasses_class, self._unstructure_dataclasses)
        self.register_structure_hook_func(
            _is_dataclasses_class, self._structure_dataclasses)

    def _unstructure_dataclasses(self, obj):
        """Our version of `attrs.asdict`, so we can call back to us."""
        fields = dataclasses.fields(obj)
        dispatch = self._unstructure_func.dispatch
        rv = self._dict_factory()
        for f in fields:
            name = f.name
            v = getattr(obj, name)
            rv[name] = dispatch(v.__class__)(v)
        return rv

    def _structure_dataclasses(self, obj, cl):
        """Instantiate an attrs class from a mapping (dict)."""
        # For public use.
        conv_obj = {}  # Start with a fresh dict, to ignore extra keys.
        dispatch = self._structure_func.dispatch
        for f in dataclasses.fields(cl):  # type: ignore
            # We detect the type by metadata.
            type_ = f.type
            name = f.name

            try:
                val = obj[name]
            except KeyError:
                continue

            if name[0] == "_":
                name = name[1:]

            conv_obj[name] = (
                dispatch(type_)(val, type_) if type_ is not None else val
            )

        return cl(**conv_obj)  # type: ignore