How to make a proxy object with typing as underlying object in python

Question

I have a proxy class with an underlying object. I wish to pass the proxy object to a function that expects and underlying object type. How do I make the proxy typing match the underlying object?

class Proxy:
    def __init__(self, obj):
        self.obj = obj

    def __getattribute__(self, name):
        return getattr(self.obj, name)

    def __setattr__(self, name, value):
        setattr(self.obj, name, value)

def foo(bar: MyClass):
    ...

foo(Proxy(MyClass())) # Warning: expected 'MyClass', got 'Proxy' instead

Answer 1

Credit to @SUTerliakov for actually providing the essence of this answer in the comment on the question. The code should look something along the lines of the following:

from typing import TYPE_CHECKING
from my_module import MyClass

if TYPE_CHECKING:
    base = MyClass
else:
    base = object


class Proxy(base):
    def __init__(self, obj):
        self.obj = obj

    def __getattribute__(self, name):
        return getattr(self.obj, name)

    def __setattr__(self, name, value):
        setattr(self.obj, name, value)


def foo(bar: MyClass):
    ...

foo(Proxy(MyClass())) # Works!

Note that your class may not always be available - but that's no real problem. The trick works perfectly fine with TypeVars.

# proxy.py
from typing import TYPE_CHECKING, TypeVar


Proxied = TypeVar('Proxied')
if TYPE_CHECKING:
    base = Proxied
else:
    base = object


class Proxy(base):
    def __init__(self, obj: Proxied):
        self.obj = obj

    def __getattribute__(self, name):
        return getattr(self.obj, name)

    def __setattr__(self, name, value):
        setattr(self.obj, name, value)

And in the file where you use it:

from proxy import Proxy


def foo(bar: MyClass):
    ...

foo(Proxy(MyClass())) # Works!