Add typed attribute to third party class.

Feature

I would like to be able to add a (typed) attribute to a third-party class instance.

To give a specific example, Flask's current_app, and Flask-AppBuilder. Some example code:

    def my_view(self):
        reveal_type(current_app.appbuilder)
        if current_app.appbuilder.sm.has_access(...):
            ...

The reveal_type here shows Any: airflow/www/views.py:850: note: Revealed type is 'Any'

Things I tried:

1. To add a typed attribute myself:

   if TYPE_CHECKING:
       current_app.appbuilder = AppBuilder(None)
       reveal_type(current_app.appbuilder)
   

   Didn't work: airflow/www/views.py:115: note: Revealed type is 'Any'

2. A partial type stub file

   I could use stubgen etc to create a stub file for all of flask and then edit the type in flask.globals, but this presents a maintenance burden that I don't want (keeping it in sync).

   I searched for any way I could to have a "partial" stub file -- if I could have a stubs/flask/globals.pyi with out neededing all the rest of the type stubs for this module, but couldn't get it working - likely not supported.

Pitch

I don't know what the feature would look like, but for the flask ecosystem it is fairly common to add properties on to the global flask object, or the g global variable, and I would love to be able to type-check my use of them, without needing to cast it at each use.

This issue is mostly a request for help/ "is there any sensible way of doing this?"

まず、airflow/www/views.py:850 の reveal_type の結果と、115 行目付近の TYPE_CHECKING の試行を再現します。Flask's flask.globals の型と stubgen がサードパーティ属性をどのように扱うかを確認します。Issue に、文書化された保守可能なアプローチ、または完全な置き換え用スタブなしでそのような属性を型付けするための、明確にスコープが定められた type-checker 機能があれば完了です。