optional private list parameters shows warning

[Speedy1991]

This shows a warning on _panels in pycharm:

import strawberry


@strawberry.type
class PanelType:
    id: strawberry.ID


@strawberry.type
class PageType:
    _panels: strawberry.Private[list[PanelType] | None] = None

    @strawberry.field
    def panels(self, info: strawberry.Info) -> list[PanelType]:
        return self._panels


@strawberry.type
class Query:
    @strawberry.field
    def hello(self, info: strawberry.Info) -> PageType:
        return PageType(_panels=[PanelType(id=strawberry.ID('a'))])

Also confirmed with pyright

error: Type "Private[list[PanelType] | None]" is not assignable to return type "list[PanelType]"
    Type "Private[list[PanelType] | None]" is not assignable to type "list[PanelType]"
      "None" is not assignable to "list[PanelType]" (reportReturnType)
1 error, 0 warnings, 0 informations 

[wimble3]

@Speedy1991, seems that you always try to pass _panels to PageType constructor as a list, it can be empty list or not. Also you have wrong annotation to panels field, maybe its better to use classic dataclass annotation Something | None = None. Try this, for example:

import strawberry


@strawberry.type
class PanelType:
    id: strawberry.ID


@strawberry.type
class PageType:
    panels: strawberry.Private[list[PanelType]] | None = None


@strawberry.type
class Query:
    @strawberry.field
    def hello(self, info: strawberry.Info) -> PageType:
        return PageType(panels=[PanelType(id=strawberry.ID('a'))] or None)

[erikwrede]

Hey @Speedy1991, from the font I assume you're using a JetBrains IDE. This removes the error:

@strawberry.type
class PanelType:
    id: strawberry.ID

@strawberry.type
class PageType:
    _panels: strawberry.Private[list[PanelType] | None]

    @strawberry.field
    def panels(self, info: strawberry.Info) -> list[PanelType]:
        return self._panels

@strawberry.type
class Query:
    @strawberry.field
    def hello(self, info: strawberry.Info) -> PageType:
        return PageType(_panels=[PanelType(id=strawberry.ID('a'))])

MyPy does not show any issues for your snippet in either version, so I strongly assume this is caused by PyCharm.

[Speedy1991]

Hey @wimble3, thanks for the hint, but i already tried this and it still shows the same error. See this confirmation:

Hey @erikwrede
This works if _panels are defined. As soon as I call it with an empty constructor, this will crash with 'PageType.init() missing 1 required keyword-only argument: '_panels'`

See this playground: https://play.strawberry.rocks/?gist=d3d11c5d5b0b7af7932b4299c03910fb

[Speedy1991]

Also note, this is not a pycharm only problem, this also fails with the CLI of pyright

[wimble3]

@Speedy1991 Its not my full example. Btw i checked it in pycharm. You need to change your return statement to return PageType(panels=[PanelType(id=strawberry.ID('a'))] or None)

[wimble3]

@Speedy1991 But anyway its seems so strange =)

[Speedy1991]

That specific line of code will always give you a list with one panel, as the or None part doesn't change anything since the list is never empty. Adding this change will lead to another warning for unreachable code :)

[Speedy1991]

however i think i know what you mean:

this feels like boilerplate

---

IMO this is still the correct way to use the type anotations, because the private is like a proxy and all "real" definitions are defined in the Private Generic.
_panels: strawberry.Private[list[PanelType] | None] = None

[wimble3]

@Speedy1991 hm, its interesting posiition about proxy, so, maybe its more correct variant?

class PageType:
    panels: strawberry.Private[list[PanelType] | None] = strawberry.Private[None]

May you please tell why you need optional param here if you always have a non empty list at your constructor call?

[Speedy1991]

@wimble3, thank you for your prompt response. I've tested the proposed solution, and it appears the issue persists specifically with empty constructors when dealing with iterables.

Please refer to the following Strawberry Playground link, which demonstrates the problem:
https://play.strawberry.rocks/?gist=459eee1deacdb99b13208b41f843563b

This behavior is exclusively observed with iterable types (or types that behave as such). Primitive types like int or str function correctly; for example, _my_secret: strawberry.Private[str | None] = None does not exhibit this issue.

May you please tell why you need optional param here if you always have a non empty list at your constructor call?

The fundamental reason is a lack of direct control over the underlying data source. The _panels field can originate as null, undefined, or a list[PanelType]. Panel data is populated via two primary methods: a static method or direct manual assignment.
E.g:

@strawberry.type
class PageType:
    _panels: strawberry.Private[list[PanelType] | None] = None

    @strawberry.field
    def panels(self, info: strawberry.Info) -> list[PanelType]:
        return self._panels

    @classmethod
    def from_obj(cls, page: Page): # <--- page is a db object
        return PageType(_panels=[PanelType(....) for panel in page.panel_set.all(), ...) # this is example code, the real case is a bit more complex :)

While from_obj handles database-driven page creation, there are scenarios where PageType instances are statically created (e.g., predefined introduction pages), bypassing the database object and necessitating the flexibility of an optional _panels field.

While I could likely enforce a list (and skip optional None's), my core concern remains: this appears to be a typing bug with Private list defaults. I believe it should function correctly regardless of my individual use case, even if a workaround exists.

[Speedy1991]

Ah i found another example:
_panel_uuid: strawberry.Private[uuid.UUID | None] = None

[wimble3]

@Speedy1991 Ok, my bad, ure right