Can we assign an object to a callable (or to a function) in python?

Introduction: We know that, in python, a function is a class. To some extent, We can look at it as a data type which can be called and return a value. So it is a callable. We also know that Python classes are callables. When they are called, we are actually making objects as their instances.

My implementation: In a current task, I have defined the following class with two methods:

class SomeClass():
   def some_method_1():
      some_code
   def some_method_2():
      some_code
      self.some_method_1()
      some_code

To describe the code above, some_method_2 is using some_method_1 inside it. Now I am seeking to test some_method_2. In this case, I need to replace some_method_1 with a mock object and specify the mock object to return what I define:

from unittest.mock import Mock
import unittest

class TestSomeClass(unittest.TestCase):
   some_object=Some_Class()
   some_object.some_method_1 = Mock(return_value=foo)
   self.assertEqual(an_expected_value, some_object.some_method_2())

This works totally fine and the script runs without error and the test result is also ok.

A fast Intro about Mypy: Mypy is a python type checking tool which can run and check if the script is written correctly based on variable types. It does this process by some criteria such as type annotations, variable assignments and libraries stub files. This process is done without interpreting and running the code.

What is the Problem? When I try to check my code with mypy, it gives error for this line:

some_object.some_method_1 = Mock(return_value=foo)

The error indicates that I am not allowed to assign an object to a callable in python. Sometimes mypy does not report real errors and I doubt if this is the case. Especially because I can run my code with no problem.

Now, my question is, have I done my job wrong or just the mypy report is wrong? If I have done wrong, how can I implement the same scenario in a correct manner?