Question

The following is a sample piece of code from a program that I’m referring to. I realized that I hadn’t truly this concept, so I’m asking here.

class Chef(games.Sprite):
    """
    A chef which moves left and right, dropping pizzas.
    """
    image = games.load_image("chef.bmp")

    def __init__(self, y = 0, speed = 2, odds_change = 200):
        """ Initialize the Chef object. """
        super(Chef, self).__init__(image = Chef.image,
                                   x = games.screen.width / 2,
                                   y = 55,
                                   dx = speed)

        self.odds_change = odds_change
        self.time_til_drop = 0

This is what I thought is the case:

the sixth line def __init__(self, y = 0, speed = 2, odds_change = 200) gives the object its initial values and the values enclosed in the kernel:

super(Chef, self).__init__(image = Chef.image, x = games.screen.width / 2, y = 55,dx = speed) deal with these values of the object after initialization. Making the sixth line values fairly arbitary. For example I was able to change the value of y in the sixth line constructor to any arbitary number, and the object stayed in the same y coordinate on the screen. Is my understanding of this correct?

Answer 1

What super actually does is calls the parent class’ corresponding method. http://docs.python.org/library/functions.html#super
So, in your case, you are calling the __init__ method of the class games.Sprite from your defined class Chef

The reason you got the object at the same position although you changed y in the sixth line because you didn’t change the parameter y=55 which you are passing to the super function. If you will change this y to something else, your object will definitely move.

The general practice while using super is to pass the same parameters as you get from the __init__ method. In your code, you are not passing any of the parameters of __init__ to super(Chef, self).__init__ and hence the parameters defined in __init__ are more or less meaningless. So your code should be some what like this –

class Chef(games.Sprite):
    """
    A chef which moves left and right, dropping pizzas.
    """
    image = games.load_image("chef.bmp")

    def __init__(self, x = games.screen.width / 2, y = 55, speed = 2, odds_change = 200):
        """ Initialize the Chef object. """
        super(Chef, self).__init__(image = Chef.image,
                               x = x,
                               y = y,
                               dx = speed)     # although this will work, you should either rename dx as speed or vice-versa

        self.odds_change = odds_change
        self.time_til_drop = 0

Rem, you can take more parameters in the __init__ method then you pass to super(Chef, self).__init__ function.