Confusion about TypeError and 'self'

[Muzzrooms]

Hey everyone, this is my first post so I hope this is clear.
I am working on some code where the user is asked to select from a comboBox.

This problem I have is the code is suggesting I need to include the self argument however when I include it, it still errors out. I've gone around in circles for a couple of days now. Your insights would be greatly appreciated.

WITHOUT SELF ARGUMENT

    def play(self):
        guess = str(self.ui.comboBox.currentText())
        return guess

    if play() == comp_num:
        winmessage()
    else:
        losemessage()

And this is the Error

Error:
Traceback (most recent call last):
  File "D:/Muzzrooms/Desktop/Year 11/Term 2/Digital Solutions/Guessing Game/Guessing_game_completed.py", line 15, in <module>
    class MainWindow:
  File "D:/Muzzrooms/Desktop/Year 11/Term 2/Digital Solutions/Guessing Game/Guessing_game_completed.py", line 43, in MainWindow
    if play() == comp_num:
TypeError: play() missing 1 required positional argument: 'self'

WITH SELF ARGUMENT

    def play(self):
        guess = str(self.ui.comboBox.currentText())
        return guess

    if play(self) == comp_num:
        winmessage()
    else:
        losemessage()

And this is the error I receive if I include the self argument.

Error:
Traceback (most recent call last):
  File "D:/Muzzrooms/Desktop/Year 11/Term 2/Digital Solutions/Guessing Game/Guessing_game_completed.py", line 15, in <module>
    class MainWindow:
  File "D:/Muzzrooms/Desktop/Year 11/Term 2/Digital Solutions/Guessing Game/Guessing_game_completed.py", line 43, in MainWindow
    if play(self) == comp_num:
NameError: name 'self' is not defined

Your help is greatly appreciated;
-Muzzrooms