classes, inheritance [beginner] Python

Question

Hey I'm new to this python thing. Have few days to learn all about classes but at the beginning I have problem. I got this kind of error TypeError: __init__() missing 1 required positional argument: 'nazwa'. Can you help me with solution? I want to print out calculation for my object.

class Figura(object):
    def __init__(self,nazwa):
        self.nazwa = nazwa
    def calculate(self):
        print(self.nazwa)

class Kolo(Figura):
    def __init__(self,nazwa,promien):
        Figura.__init__(self)
        self.promien = promien

    def calculate(self):
        Figura.calculate(self)
        print(2 * 3.1415 * promien)

kolo1 = Kolo('kolo',4)
kolo1.calculate()

Martijn Pieters · Accepted Answer · 2015-11-22 13:02:52Z

You'll need to pass on the nazwa argument in the Kolo.__init__() method call:

class Kolo(Figura):
    def __init__(self, nazwa, promien):
        Figura.__init__(self, nazwa)
        self.promien = promien

You may want to use the super() function there instead and avoid having to repeat the parent class:

class Kolo(Figura):
    def __init__(self, nazwa, promien):
        super().__init__(nazwa)
        self.promien = promien

    def calculate(self):
        super().calculate()
        print(2 * 3.1415 * self.promien)

Note that I corrected your Kolo.calculate() method as well; you want to refer to self.promien rather than make promien a local name.

Demo:

>>> class Figura(object):
...     def __init__(self,nazwa):
...         self.nazwa = nazwa
...     def calculate(self):
...         print(self.nazwa)
...
>>> class Kolo(Figura):
...     def __init__(self, nazwa, promien):
...         super().__init__(nazwa)
...         self.promien = promien
...     def calculate(self):
...         super().calculate()
...         print(2 * 3.1415 * self.promien)
...
>>> kolo1 = Kolo('kolo',4)
>>> kolo1.calculate()
kolo
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