7. Instance Methods

When you define a function inside a class, and call the function via an instance of a class, the function is a method. e.g game.level_up() below.
The method, def level_up(self), has the first argument, (self).
Python automatically passes the object to the method as the first argument.

7.1. Regular Methods without parameters

In the code below, game.level_up() calls the method level_up.
self.game_level += 1 adds 1 to self.game_level.
When calling the method on the game object, game.level_up(), self is not written in the parentheses since it is automatically passed.
The first print statement outputs 1, since the game object is instantiated with a game_level of 1 via game = LevelGame(game_level=1).
Then, after the level_up() method has been called via game.level_up(), the second print statement outputs 2.
In the code below
class LevelGame:
    def __init__(self, game_level):
        self.game_level = game_level

    def level_up(self):
        self.game_level += 1

game = LevelGame(game_level=1)
print(game.game_level)

game.level_up()
print(game.game_level)

Tasks

  1. Check that print output above is 1, then 2.

  2. Modify the level_up function in the previous example so that the level can’t go above 10. Hint: use the max function.

  3. Modify the code so that the LevelGame.game_level starts at 10 then goes down by 1 when a level_down function is called.

  4. Modify the level_down function in the previous example so that the level can’t go below 0. Hint: use the min function.

7.2. Regular Methods with parameters

In the code below, game.set_speed(5) calls the method set_speed to set the variable self.game_speed to 5.
game = SpeedGame(1) initializes the game speed to 1.
The print statement outputs 1.
game.set_speed(5) sets the game speed to 5.
The print statement outputs 5.
class SpeedGame:
    def __init__(self, game_speed):
        self.game_speed = game_speed

    def set_speed(self, game_speed):
        self.game_speed = game_speed

game = SpeedGame(1)
print(game.game_speed)

game.set_speed(5)
print(game.game_speed)

Tasks

  1. Modify the set_speed function so that any speed values passed in are limited to a maximum speed of 10. Hint: use the max function.

  2. Modify the set_speed function so the speed must be between 0 and 10. Hint: use the min and max functions.