Access to type of methods of an object through weakref proxy

In this kind of examples

import weakref

var: str = "Hello World!"
proxy_var: weakref.ProxyType[str] = weakref.proxy(var)
var2 = proxy_var.upper()

I would like that my type checker detect that var2 is a str object (and in general I would like to have the auto-completion after proxy_var.)

I don’t really know if this is possible in python so I am asking here.

Thank you