Patch a dataclass attribute which is dynamically generated in its dependency in unit testing

I am new to Unit testing. I have used mocking, patching in the past but the case I have is a little bit complicated for me to create unit tests.

So I have a file: parent.py with the following data class

import multiprocessing
from dataclasses import dataclass

@dataclass
class ParentClass:
    cpu_count: int = multiprocessing.cpu_count() 

I have another module child.py with the following data class

from stackoverflow.parent import ParentClass
from dataclasses import dataclass

@dataclass
class ChildClass(ParentClass):
      some_attribute_1: int = 1
      some_attribute_2: int = 2
      ....

Finally, I have a third module actual_function.py that uses these data classes.

from stack_overflow.child import ChildClass


def get_cpu_count_and_attributes(cc: ChildClass):
    return cc.cpu_count, cc.some_attribute_1 

Here, I want to unit test print_cpu_count_and_attributes function. How does patching work here? I created the following test case and it fails. The cpu_count in my system is 16 but I want to mock it with return value 8 so that it works on other machines with different number of cores

from unittest import mock
from stack_overflow.actual_function import *
from stack_overflow.child import ChildClass


@mock.patch('stack_overflow.parent.multiprocessing.cpu_count', return_value=8)
def test_print_cpu_count_and_attributes():
    cc = ChildClass()
    assert get_cpu_count_and_attributes(cc) == (8, 1)

Here is the folder structure.

stackoverflow
├── __init__.py
  ├── actual_function.py
  ├── child.py
  ├── parent.py
  └── test_function.py