class Building:
    def __init__(self, building_no):        #konstruktor
        self.building_no = building_no
        self.staircases = []

    def add_staircase(self, staircase):
        self.staircases.append(staircase)

    def print_all_staircases(self):
        for staircase in self.staircases:
            print("Staircase nr: " + staircase.staircase_no)

    def building_number(self):
        print('Building number is', self.building_no)


class Staircase:
    def __init__(self, staircase_no):
        self.staircase_no = staircase_no

    def staircase_number(self):
        return self.staircase_no

building = Building("P2")
staircase_1 = Staircase("5")

print(building.print_all_staircases())

building.add_staircase(staircase_1)

print(building.print_all_staircases())