Python ctypes breaks on include iostream

Question

I am using python ctypes to call a function in c++ from python. Currently, I have the following c++ file:

five.cpp

extern "C" {
    int get_five(){
        return 5;
    }
}

And python file:

five.py

import ctypes
from pathlib import Path


lib = ctypes.CDLL(Path(Path.cwd(),'five.dll').as_posix())
print(lib.get_five())

Which works and prints the number 5 when i run it.

However, as soon as I include any headers in the c++ file, it breaks down. So if I change the file to:

#include <iostream>
extern "C" {
    int get_five(){
        return 5;
    }
}

It breaks, and I get the following error:

FileNotFoundError: Could not find module '...\five.dll' (or one of its dependencies). Try using the full path with constructor syntax.

I am compiling on Windows, with the following command:

g++ -shared five.cpp -o five.dll

I am probably missing something obvious, since I am very new to programming in c++. However, I can't seem to find what it is.