4.4 Using class variables

You can use a class variable to keep track of the number of rooms you have in your game.

First, add a class variable to the Room class, outside the constructor.

class Room():

    number_of_rooms = 0

To use a class variable you use the name of the class, as opposed to the name of an object, for example:

Room.number_of_rooms = 1

Each time a Room object is created, you can increment the number_of_rooms class variable in the constructor to keep track of the rooms created.

class Room():

    number_of_rooms = 0

    def __init__(self, room_name):

        ...

        Room.number_of_rooms = Room.number_of_rooms + 1

Regardless of how many rooms are created, the total number will be available in the class variable Room.number_of_rooms.

kitchen = Room("kitchen")

ballroom = Room("ballroom")

dining_hall = Room("dining hall")

print("There are " + str(Room.number_of_rooms) + " rooms to explore.")

• How do you think class variables might be of use to you in creating your game?

• Can you think of any other situations in which you would need a variable to be shared by all instances of a class?