Your code is missing a closing ) on the last line, so if you try to run your code as-is you'll get an error from that.

However, assuming you fix that, running this code with Python 3 will complete successfully, but will not give any output. You are defining a class and a couple of methods, but you never instantiate the class or call any of the methods. Even if you did, though, you'd get an error as brennstunden_im_tag is not defined anywhere, so you'll get an error trying to run stromkosten_pro_jahr(). You also need to have self as the first parameter for any class method. Finally, stromkosten_pro_jahr() should return the value, not print() it. Here is an example of what your code should look like:

class Strom(object):

    def __init__(self, brennstunden_im_tag):

        self.preis_kilowattstunde = 0.21

        self.brennstunden_im_tag = brennstunden_im_tag



    def stromkosten_pro_jahr(self, watt):

        '''

        (integer) -> float



        leitet aus einer Zahl in Watt eines Objektes die Stromkosten pro Jahr ab

        '''

        return watt * self.brennstunden_im_tag * 365 * self.preis_kilowattstunde / 1000



    def stromkosten_differenz(self, watt_objekt1, watt_objekt2):

        '''

        (integer, integer) -> float



        Nimmt die Stromkosten in Watt zweier Objekte und gibt die Stromkostendifferenz in CHF aus.

        '''

        if watt_objekt2 > watt_objekt1:

            print(self.stromkosten_pro_jahr(watt_objekt2) - self.stromkosten_pro_jahr(watt_objekt1))

        else:

            print(self.stromkosten_pro_jahr(watt_objekt1) - self.stromkosten_pro_jahr(watt_objekt2))





if __name__ == "__main__":

    my_strom = Strom(10)

    my_strom.stromkosten_differenz(100, 50)

This returns 38.325 - hopefully that's the result you're looking for.