Annotate Return Type On Enum Function

I defined the following StrEnum class to capture the canonical set of valid values for a storage format in py-vmt. It includes a default function that can be called to get what the system considers the default storage format.

class StorageFormat(StrEnum):
    SQLITE = "sqlite"
    JSON = "json"

    @staticmethod
    def default():
        return StorageFormat.SQLITE

This works, but what is missing is a type annotation for the return value of default.

I'd like to use StorageFormat as the return type annotation. However, the annotations are eagerly evaluated at the time the function definition is being processed. The StorageFormat class is not fully evaluated at that point and so isn't available.

Instead, what I can do is quote StorageFormat as a string to make it a forward reference.

class StorageFormat(StrEnum):
    SQLITE = "sqlite"
    JSON = "json"

    @staticmethod
    def default() -> "StorageFormat":
        return StorageFormat.SQLITE

The string type annotation will be lazily evaluated at a later time when StorageFormat fully exists. This is behavior that is slated to be deprecated. And it is no longer needed as of Python 3.14 which lazily evaluates all annotations by default now.

If I want to be more specific with the above annotation, I can import Literal from typing and then wrap a specific enum value.

class StorageFormat(StrEnum):
    SQLITE = "sqlite"
    JSON = "json"

    @staticmethod
    def default() -> "Literal[StorageFormat.SQLITE]":
        return StorageFormat.SQLITE

Now it will specifically enforce SQLITE rather than accepting SQLITE or JSON.