class fixa:
    barva = ""
    def pis(self):
        print("Pisu {}.".format(self.barva))   
    def __init__(self, barva=""):
        self.barva = barva
    def __str__(self):
        return("Fixa pisici {}.".format(self.barva))
    
fixa1 = fixa()
fixa1.barva = "cervene"
fixa1.pis()
print(fixa1) # print(str(fixa1))

fixa3 = fixa()
fixa3.barva = "modre"
fixa3.pis()

fixa2 = fixa("zelene")
fixa2.pis()