There are a number of libraries you could use. Here are two third party ones:
Using PyAutoGui
A powerful GUI automation library allows you to get screen size, control the mouse, keyboard and more.
To get the position you just need to use the position() function. Here is an example:
>>>import pyautogui
>>>pyautogui.position()
(1358, 146)
>>>
Where 1358 is the X position and 146 is the Y position.
Relavent link to the documentation
Using Pynput
Another (more minimalistic) library is Pynput:
>>> from pynput.mouse import Controller
>>> mouse = Controller()
>>> mouse.position
(1182, 153)
>>>
Where 1182 is the X position and 153 is the second.
Documentation
This library is quite easy to learn, does not require dependencies, making this library ideal for small tasks like this (where PyAutoGui would be an overkill). Once again though, it does not provide so many features though.
Windows Specific:
For platform dependant, but default library options (though you may still consider them overkills) can be found here: Getting cursor position in Python.