help for type hints for mixin class

[prim]

Hello.

I'm developing a game and its very heavy python code will have a mixin design similar to the one below.

I hope to mark the self parameter of Bag.add_item as Entity class. In this way, vscode can prompt to complete the log_debug function when I enter self.log_.

However, pyright will consider this kind of annotation illegal and report Type of parameter "self" must be a supertype of its class "Log"

Please help me, how should I write the type annotation for this mixin class? Or how to avoid pright reporting these errors.

class Log(object):

	def log_debug(self: "Entity", msg):
		pass

class Bag(object):

	def add_item(self: "Entity"):
		self.log_debug("")

class Entity(Bag, Log):
	pass

[erictraut]

The way this is typically done is through the use of a protocol class.

from typing import Protocol

class SupportsLogDebug(Protocol):
    def log_debug(self, msg: str): ...

class Log(SupportsLogDebug):
    def log_debug(self, msg: str):
        pass

class Bag:
    def add_item(self: SupportsLogDebug):
        self.log_debug("")

class Entity(Bag, Log):
    pass

Or if you don't want to define a separate protocol class, you could do:

from typing import Protocol

class Log(Protocol):
    def log_debug(self, msg: str):
        pass

class Bag:
    def add_item(self: Log):
        self.log_debug("")

class Entity(Bag, Log):
    pass

In general, this isn't a pattern I would recommend in object-oriented programming. The way you've defined this class hierarchy, the parent class Bag is not usable on its own. It's useful only when combined with some other functionality. Refactoring the class definitions would avoid this.

[Azureblade3808]

You can have all your mix-in classes subclass typing.Protocol and leave other code unmodified.

from typing import Protocol

class Log(Protocol):
    def log_debug(self: "Entity", msg):
        pass

class Bag(Protocol):
    def add_item(self: "Entity"):
        self.log_debug("")

class Entity(Bag, Log):
    pass