what i would like to add to subprocess.Popen()

[Gribouillis]

is cwd= the function to be called in the context of the forked child process?

I'm not sure about what this means, but I think the answer is yes because the cwd parameter does not change the working directory of the parent process. Here is what the documentation says

Output:
If cwd is not None, the function changes the working directory to cwd before executing the child. cwd can be a string, bytes or path-like object. On POSIX, the function looks for executable (or for the first item in args) relative to cwd if the executable path is a relative path.

Changed in version 3.6: cwd parameter accepts a path-like object on POSIX.

Changed in version 3.7: cwd parameter accepts a path-like object on Windows.

Changed in version 3.8: cwd parameter accepts a bytes object on Windows.