Functional Pick

[silviogutierrez]

# In pick.py
T = TypeVar("T")

def pick(target: Type[T], *, name: str, fields: List[str]) -> Type[T]:
    return target

# In plugin.py
def analyze_functional_pick(ctx: DynamicClassDefContext) -> None:
    klass = ctx.call.args[0]
    assert isinstance(klass, NameExpr)

    type_name = klass.fullname
    assert type_name is not None

    qualified = ctx.api.lookup_fully_qualified_or_none(type_name)
    assert qualified is not None

    ctx.api.add_symbol_table_node(ctx.name, qualified)

This allows us to do the following, with mypy understanding it:

Opera = pick(models.Opera, fields=["name"])

And much more elaborate options over the existing syntax:

Opera = Pick[models.Opera, "name"]

[mmonj]

Functional pick seems to me a better way to create a model type alias. It could open up a way to add extra functionality such as adding extra context (like django rest framework is able to do) and to facilitate adding extra fields such as with DRF's SerializerMethodField for the cases where using a @property attribute from the model itself wouldn't be sufficient