Class

player_name = 'MuscleManShaoChun'
player_strength = 100000000
player_item = ["chicken breast", 'salad']

沒什麼問題，那就再加一個

player1_name = 'MuscleManShaoChun'
player1_strength = 100000000
player1_item = ["chicken breast", 'salad']
player2_name = 'Rick_Astley'
player2_strength = 20091025
player2_item = ["never", 'gonna', 'give', 'you', 'up']

沒什麼問題，那就再加一個

player1_name = 'MuscleManShaoChun'
player1_strength = 100000000
player1_item = ["chicken breast", 'salad']
player2_name = 'Rick_Astley'
player2_strength = 20091025
player2_item = ["never", 'gonna', 'give', 'you', 'up']
player3_name = 'NoName'
player3_strength = 47
player3_item = ["NameChangeCard", 'cheatsheet']

越來越多，有點麻煩…

學過的:dictionary

player1 = {'name':'MuscleManShaoChun',
           'strength': 100000000,
           'item': ["chicken breast", 'salad']}

新的酷東西: Class!

Class 是啥

• 中文：類別
• 基本上是自己創造一個物件(資料型態)
• 把函數跟變數結合的工具
• 模板
• 可以用來建tree, heap之類的資料結構

Class 怎麼定義

class Player:
    pass

Class 怎麼用

跟函數定義的方式很像

class Player:
    pass
    
player1 = Player()
player1.name = "MuscleManShaoChun"
player1.strength = 100000000
player1.item = ["chicken breast", 'salad']
 
player2 = Player()
player2.name = 'Rick_Astley'
player2.strength = 20091025
player2.item = ["never", 'gonna', 'give', 'you', 'up']

這似乎沒有比較簡單

Class 裡面也可以放函數,變數或class

class Player:
    def set_variables(name, strength, items):
        Player.name = name
        Player.strength = strength
        Player.items = items
    
    def change_name(new_name):
        Player.name = new_name
    
        
player1 = Player()
player1.set_variables("MuscleManShaoChun", 100000000, ["chicken breast", 'salad'])
player2 = Player()
player2.set_variables('Rick_Astley', 20091025, ["never", 'gonna', 'give', 'you', 'up'])

哈哈笑死是不是出bug了

TypeError: set_variables() takes 3 positional arguments but 4 were given

酷酷的新名詞

• method(方法): class裡面的function
• instance(實體): 依照class做出來的物件
• attribute(屬性): class裡面的變數

__init__, self

self

• class裡面的method至少要有self
• 決定要設定哪一個物件

__init__

• 特殊的method
• 是一個constructor,初始化的時候用
• obj = classname()
• 一定要有self

正確的寫法

class Player:
    def __init__(self, name, strength, items):
        self.name = name
        self.strength = strength
        self.items = items
        
    def change_name(self, new_name):
        self.name = new_name
        
player1 = Player("MuscleManShaoChun", 100000000, ["chicken breast", 'salad'])
player2 = Player('Rick_Astley', 20091025, ["never", 'gonna', 'give', 'you', 'up'])
player1.change_name('SuperMuscleManShaoChun')

class phone:
    password = '0000'
    
a = phone()
b = phone()
c = phone()
print(phone.password, a.password, b.password, c.password)

'0000', '0000', '0000', '0000'

a.password = '1234'
print(phone.password, a.password, b.password, c.password)

'0000', '1234', '0000', '0000'

phone.password = '5678'
print(phone.password, a.password, b.password, c.password)

'5678', '1234', '5678', '5678'
為什麼a沒有跟著改

用vars()看attribute

vars(a) #{'password':'1234'}
vars(b) #{}
vars(c) #{}
vars(phone) #{..., 'password':'5678'}

phone.color = 'black'
print(phone.color, a.color, b.color, c.color)

'black', 'black', 'black', 'black'

a.price = 10000
print(phone.price, a.price, b.price, c.price)

AttributeError

練習時間

利用之前的Player, 寫一個函數a.transfer_items(b)把b的items全部轉移到a, 並平分他們的strength

範例解

class Player:
    def __init__(self, name, strength, items):
        self.name = name
        self.strength = strength
        self.items = items
        
    def transfer_items(self, b):
        self.items.extend(b.items)
        self.strength = b.strength = (self.strength+b.strength)/2