[Python] Type-hinting a dynamic, asymmetric class property

I'm currently working on removing all the type errors from my Python project in VS Code.

Assume you have a Python class that has an asymmetric property. It takes any kind of iterable and converts it into a custom list subclass with additional methods.

class ObservableList(list):
"""list with events for change, insert, remove, ..."""
# ...

class MyFrame:
@property
def my_list(self) -> ObservableList:
return self._my_list
@my_list.setter
def my_list(self, val: typing.Iterable):
self._my_list = ObservableList(val)
# ...

my_frame = MyFrame()


VS Code (i.e. Pyright) will correctly deduce that:

• you can set my_frame.my_list using any iterable, and
• my_frame.my_list will always be an ObservableList.

Now, let's assume that there is no actual @property code. Instead, the property is implemented dynamically using __setattr__ and __getattr__. (Context: We're talking about a GUI generator which provides automatic bindings.)

I want to use a declaration on class level to tell the typechecker that this property exists, without actually spelling it out:

class MyFrame(AutoFrame):
my_list: ???
# ...


(AutoFrame provides the __getattr__/ __setattr__ implementation.) What can I put in place of the ??? to make this work?

• When using ObservableList, Pyright complains when I assign a plain list to the property.
• When using Iterable or list, Pyright complains when I access ObservableList-specific methods.

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