I’m currently in the process of developing a tennis-counting system for fun. Since I’m a newby in Python, I’m currently struggling with some parts of the code.

I’m trying compare the amounts of sets that a player (or both) played to the total amount of sets you can play.

Here’s part of my code:

def set():
    global listenpunkteone
    global listenpunktetwo
    global setlisteone
    global setcounter
    global scoreone 
    global scoretwo 
    if setlisteone[setcounter] < 6 and setlistetwo[setcounter] < 6:
        if scoreone == 50:
            scoreone = 0
            listenpunkteone += 1
            setlisteone[setcounter] = listenpunkteone
            print("The score is",setlisteone[setcounter],":", setlistetwo[setcounter])
            game()
        elif scoretwo == 50:
            scoretwo = 0
            listenpunktetwo += 1
            setlistetwo[setcounter] = listenpunktetwo
            print("The score is",setlisteone[setcounter],":", setlistetwo[setcounter])
            game()
    elif setlistetwo[setcounter] == 6:
        setlistetwo[setcounter] = listenpunktetwo
        print("The score is",setlisteone[setcounter],":", setlistetwo[setcounter])
        listenpunktetwo = 0
        setcounter += 1
        setlistetwo[setcounter] = setlistetwo.append(listenpunktetwo) 
        game() 
    elif setlisteone[setcounter] == 6:
        setlisteone[setcounter] = listenpunkteone
        print("The score is",setlisteone[setcounter],":", setlistetwo[setcounter])
        listenpunkteone = 0
        setcounter += 1
        setlisteone[setcounter] = setlisteone.append(listenpunkteone)
        game()

setcounter is supposed to go up by 1 any time that a set has been played (surpassing of 40 points) – it does so nicely up until the score is e.g. 6:0. After, the code just breaks and gives me the Error:

TypeError: ‘<‘ not supported between instances of ‘NoneType’ and ‘int’

Is there any other way for me to compare the specific value of a list element to an integer of my choosing?

Also I don’t understand why my code runs smoothly up until hitting 6:0 -> shouldn’t a new element be automatically be appended after reaching 6 and the process repeated?

Thank You in Advance!