list of an attrs object

[amirreza-sf80]

hi 👋
in web development it is common to ask for a list of values
for example if we have a database table called human, sometimes we want to see data about a single human, sometimes we want to see a bunch of data in one place

i have achived this goal using cattrs, but I'm wondering if my way can be improved

my code so far:

data classes:

type DataList = list

@define
class HumanDataModel:
    name: str

@define
class HumanDataModelList:
    data: Annotated[DataList, HumanDataModel]

    def __iter__(self):  # needed to unstructure as a list
        return iter(self.data)

hooks:

def data_list_structure(val, t):
    annotation = get_args(t)
    data_model: type = annotation[1]
    return [converter.structure(v, data_model) for v in val]


def data_list_structure_serializer(val, t):
    annotation = get_args(t)
    data_model: type = annotation[1]
    return [converter.structure(v, data_model) for v in val]


def data_list_unstructure(val):
    return [converter.unstructure(v) for v in val]


converter.register_structure_hook_func(
    lambda t: is_annotated(t) and get_args(t)[0] is DataList, data_list_structure
)
converter.register_unstructure_hook(DataList, data_list_unstructure)

and it's used like this:

data = Human.objects.all()  # ORM call
structure = converter.structure({"data": data}, HumanDataModelList)
unstructure = converter.unstructure(structure, list)  # has to be unstructured as a list

the main thing that bugs me is that i have to create a secone list class for each data class i have, so i was wondering if there is a built-in way of handling this that i am missing

i can probably generate the second class dynamically, but thought it's worth checking in before goin on that route

[Tinche]

My first question would be why use a dedicated class (HumanDataModelList) instead of just list[HumanDataModel]?

[amirreza-sf80]

sorry i was trying to simplify the code but foolishly left out an important part

this is for django so the data used to feed the attrs calls comes from django ORM (usually)

but django ORM objects do not implement __contains__ and __getitem__, where as i understand it cattrs uses name in obj and obj[key]

so the actuall structure hook from above looks like this:

def data_list_structure(val, t):
    annotation = get_args(t)
    data_model: type = annotation[1]
    return [converter.structure(model_to_dict(v), data_model) for v in val]

where model_to_dict is used to convert each model to a dict so converter can structure each of them

since i don't know how to register a hook for list[any_attrs_class]
i looked for something similar to make_dict_structure_fn that would work with lists but doesn't seem to exists

for refrence, the above hook creates the following data

HumanDataModelList(
    data=[
        HumanDataModel(name='john'),
        HumanDataModel(name="jane")
    ]
)

when unstructured as a list, it gives this data:

[{'name': 'john'}, {'name': 'jane'}]

[amirreza-sf80]

sorry this seems to solve it

def structure_list_with_django_models(obj, cls):
    (elem_type,) = get_args(cls)
    return [
        converter.structure(model_to_dict(item), elem_type)
        if isinstance(item, Model)
        else converter.structure(item, elem_type)
        for item in obj
    ]


def is_list_of_attrs(tp):
    return get_origin(tp) is list and hasattr(get_args(tp)[0], "__attrs_attrs__")


converter.register_structure_hook_func(
    is_list_of_attrs, structure_list_with_django_models
)

now it can be simply structured and unstructured as a list without needing a second class

    structure = converter.structure(data, list[PoetDataModel])
    converter.unstructure(structure, list[PoetDataModel])