Typeerror: Missing 1 Required Positional Argument: 'Self'

Why do I get "missing 1 required positional argument: 'self'"?

On both classes create_querauto is an instance method, meaning that the class needs to be instantiated in order to call the method.

That's why it is working with the player instance.
i.e.

class Player:
    def create_querauto(self):  
        ii=random.randrange(0,8)
        img = pygame.image.load(f"Bilder/Gegenstaende/geg{ii}.png") 
        img = pygame.transform.scale(img,(100,25)) 
        return QuerWagen(200,300,img)

player_instance = Player()
player_instance.create_querauto()  # This will work
Player.create_querauto()           # This will throw the error you see above

If you would like to method to work without instantiating the class first you can define it as a static method, using the @staticmethod decorator

This would look like:

class QuerWagen(pygame.sprite.Sprite):
    @staticmethod
    def create_querauto(): 
        ii=random.randrange(0,8)
        img = pygame.image.load(f"Bilder/Gegenstaende/geg{ii}.png") 
        img = pygame.transform.scale(img,(100,25)) 
        return QuerWagen(200,300,img)

Now you can call that function on the class directly like you were trying to do.

querwagen = QuerWagen.create_querauto() # works fine

Python class showing "missing 1 required positional argument: 'self'"

You should call the method on the instance not the class object.

john_smith.f_salary()
john_smith.display()

Because the self parameter is a reference to the class instance which called the method in the first place.

Type Error missing 1 required positional argument: 'self' calling the class function

Static method use only the namespace of the class. It can use class variables but not the ones specific to an object (self).

If all of them are static methods, then you should change the code as follows because there is no notion of self in static methods.

class Interface:
    users_list = []
    admins_list = []
    categories_list = []
    current_user = ''
    user_flag = 0

    @staticmethod
    def start_menu():
        print('Add user')
        Interface.create_user()
        Interface.show_menu()

    @staticmethod
    def create_user():
        # code....

    @staticmethod
    def choose_user():
        # code...

# call
Interface.start_menu()

If you need self, make those methods instance methods by removing the staticmethod decorator. Also, since you have no arguments for the constructor you can make those variables static, like above.

class Interface:

    def __init__(self):
        self.users_list = []
        self.admins_list = []
        self.categories_list = []
        self.current_user = ''
        self.user_flag = 0

    def start_menu(self):
        print('Add user')
        self.create_user()
        self.show_menu()

    def create_user(self):
        # code....

    def choose_user(self):
        # code...

# call
inter = Interface()
inter.start_menu()

Due to the above-mentioned constraints, an instance method (method referring to the object, i.e., self) can call static methods but not vice-versa.

TypeError at / save() missing 1 required positional argument: 'self'

Views.py

def cash_in(request, amount):
    # user whose total_amount is to be updated.
    user = request.user

    # get current user instance of balance_data
    user_current_balance = balance_data.objects.get(user=user)

    # update total_amount by adding amount to its total_amount
    user_current_balance.total_amount = user_current_balance.total_amount + amount

    # save changes to database
    user_current_balance.save()
    return HttpResponse(user_current_balance.total_amount)

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