Add support for type-based transformations about dacite HOT 4 CLOSED

I have two use-cases that I wouldn't be able to handle anymore if old transform is gonna gone and a new one will be there.

First one: transform missing string value to default enum field

class SomeEnum(Enum):
    one = auto()
    two = auto()
    default_value = auto()

@dataclass
class SomeData:
    some_field: SomeEnum

def _transform_some_field(some_field: Optional[str]):
    if not some_field:
        return SomeEnum.default_value
    return SomeEnum[some_field]

dacite.from_dict(SomeData, data, dacite.Config(
    transform={'some_field': _transform_some_field}
))

Second one: transform Optional[List[str]] to Optional[List[UUID]]:

@dataclass
class SomeData:
    some_list: Optional[List[UUID]]

def _transform_some_list(some_list: Optional[List[str]]):
    if not some_list:
        return []
    return [UUID(value) for value in some_list]

dacite.from_dict(SomeData, data, dacite.Config(
    transform={'some_list': _transform_some_list}
))

In theory, second use-case can be solved with smarter cast logic (or maybe already solved), but for the first one it requires some transformation. It would be nice to have a config option to pre-process the whole data object like this:

def _preprocess_data(data: dict):
    if not 'some_field' in data:
        return data['some_field'] = SomeEnum.default_value
    return data

dacite.from_dict(SomeData, data, dacite.Config(
    preprocess=_preprocess_data
))

This way the old transformation logic wouldn't be needed for my use-cases.

from dacite.

@condemil thank you for your feedback, could provide me also example of data dicts? It will be easier for me to check how it works with new implementation. I think that both cases could be covered (first one with default value for field, second with new implementation of transform)

from dacite.

You can think of a third-party forum or chat http API where you receive information about the user, the cases can be that user_type either moderator, or admin or can be not present at all in the json object for normal user. In this case in your enum you would like to have all three options.

from dacite.

@rominf I think that you will be able to handle both cases with new transform implementation (check #55), simple like that: Config({UUID: UUID}) or Config({SomeEnum: _transform_some_field}).

from dacite.