changed 4 years ago  
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Class slide ver.

bearrrrrrro 2020/5/23
sylveon 2021/5/7 修改

語法

class ClassName:
    pass

加上一些東西

class Computer:
    pass

cp_1 = Computer()
cp_1.cpu = 'i5-8750'
cp_1.size = 14
cp_1.price = 20000

cp_2 = Computer()
cp_2.cpu = 'i7-1450'
cp_2.size = 10
cp_2.price = 2000

試試看

print(cp_1)
print(cp_1.cpu)
print(cp_2.price)

作用

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  • 好懂
  • 易讀
  • 減少重複性高的程式碼
  • 看起來比較專業 XD

概念

  • 可以發揮你的想像力做出幾乎任何東西
  • 自定義物件（資料型態？）
  • 當你想把某些狀態（資料）和功能（函式）綁在一起時，class是一個好選擇

一些不知道不影響你打code但是知道比較好的東西

  • class 又稱為「類別」
  • class 底下的資料又稱為「屬性」
  • class 底下的函式又稱為「方法 (method)」

更多簡單的範例

電腦

class Computer:
    def __init__(self, cpu, size, price):
        self.cpu = cpu
        self.size = size
        self.price = price
  • 其中__init__是比較特殊的函式，會在「建構物件」時自動呼叫（後面有範例）
  • 這裡的 xxx.yyy指"xxx的yyy"，有點類似之前在import一些工具中的用法

人

class Person:
    def __init__(self, name, height, weight):
        self.name = name
        self.height = height # cm
        self.weight = weight # kg
    def get_bmi(self):
        return self.weight / (self.height / 100) ** 2

baba

class Baba:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def up(self):
        self.x -= 1
    def down(self):
        self.x += 1
    def left(self):
        self.y -= 1
    def right(self):
        self.y += 1

Remark: class中的函式第一個參數要放self，不然可能會噴錯或是發生奇怪的事情（？

Remark: __init__中參數的名稱可以任意，像是我也可以這樣寫

class Animal:
    def __init__(self, x):
        self.name = x

但名稱不一致可能造成混淆而且沒有必要，除了可以少打幾個字以外沒有任何好處

用class

Instance

Instance 又稱為「實體」，依照class真的某個東西做出來

Class Instance
設計圖 真正的東西

有了class以後，我們可以造出多個狀態和功能類似的東西

cp_1 = Computer('i5-8750', 14, 20000)
cp_2 = Computer('i7-1450', 10, 2000)
print(cp_1)
print(cp_1.cpu)
print(cp_2.price)

bearrrrrrro = Person('bearrrrrrro', 170, 71)
print(bearrrrrrro.name)
print(bearrrrrrro.get_bmi())

連連看

解答

練習1

小明不小心把墨水打翻在他的code上，請幫小明通靈被墨水蓋掉的資訊

class Student:
    def __init__(self, name, math, english, chinese):
        墨墨墨墨墨
        墨墨墨墨墨
        墨墨墨墨墨
        墨墨墨墨墨
    def average(墨墨墨墨墨墨
        墨墨墨墨墨 # 回傳三科的平均值
    def is_pass(墨墨墨墨墨墨
        墨墨墨墨墨 # 每一科都不低於60分就回傳true
        
boss = Student('Sophia', 80, 100, 100)
print(boss.average())
print(boss.is_pass())

class Student:
    def __init__(self, name, math, english, chinese):
        self.name = name
        self.math = math
        self.english = english
        self.chinese = chinese
    def average(self):
        return sum((self.math, self.english, self.chinese)) / 3 # 回傳三科的平均值
    def is_pass(self):
        return min((self.math, self.english, self.chinese)) >= 60 # 每一科都不低於60分就回傳true
    
boss = Student('Sophia', 1000, 100, 100)
print(boss.average())
print(boss.is_pass())

特殊方法(補充) + 練習2

from math import gcd
class Rational:
    def __init__(self, p, q):
        t = gcd(p, q)
        p, q = p // t, q // t
        self.p = p
        self.q = q
    def __str__(self):
        return '{}/{}'.format(self.p, self.q)
    def __add__(self, a):
        # print('{} + {}'.format(self, a))
        nu = self.p * a.q + a.p * self.q
        di = self.q * a.q
        com = gcd(nu, di)
        return Rational(nu // com, di // com)

    # Your part here!!
    def __sub__(self, a): # x - y
        # print('{} - {}'.format(self, a))
        pass
    def __mul__(self, a): # x * y
        # print('{} * {}'.format(self, a))
        pass
    def __truediv__(self, a): # x / y
        # print('{} / {}'.format(self, a))
        pass
    def __eq__(self, a): # x == y
        # print('{} == {}'.format(self, a))
        pass

if __name__ == '__main__': 
    r = Rational(1, 4)
    s = Rational(3, 8)
    t = Rational(2, 8)

    print(r + s)
    print(r - s)
    print(r * s)
    print(r / s)
    print(r == s)
    print(r == t)

解答

from math import gcd
class Rational:
    def __init__(self, p, q):
        t = gcd(p, q)
        p, q = p // t, q // t
        self.p = p
        self.q = q
    def __str__(self):
        return '{}/{}'.format(self.p, self.q)
    def __add__(self, a):
        # print('{} + {}'.format(self, a))
        nu = self.p * a.q + a.p * self.q
        di = self.q * a.q
        com = gcd(nu, di)
        return Rational(nu // com, di // com)

    # Your part here!!
    def __sub__(self, a): # x - y
        # print('{} - {}'.format(self, a))
        nu = self.p * a.q - a.p * self.q
        di = self.q * a.q
        return Rational(nu, di)
        
    def __mul__(self, a): # x * y
        # print('{} * {}'.format(self, a))
        nu = self.p * a.p
        di = self.q * a.q
        return Rational(nu, di)
    
    def __truediv__(self, a): # x / y
        # print('{} * {}'.format(self, a))
        nu = self.p * a.q
        di = self.q * a.p
        return Rational(nu, di)
    
    def __eq__(self, a): # x == y
        # print('{} == {}'.format(self, a))
        return self.p == a.p and self.q == a.q
    
if __name__ == '__main__': 
    r = Rational(1, 4)
    s = Rational(3, 8)
    t = Rational(2, 8)
    
    print(r + s) # Ratinal.__add__(r, s)
    print(r - s)
    print(r * s)
    print(r / s)
    print(r == s)
    print(r == t)

繼承(補充)

class Dog:
    def __init__(self, name, color):
        self.name = name
        self.color = color
    def sound(self):
        print("Woof")
        
class Cat:
    def __init__(self, name, weight):
        self.name = name
        self.weight = weight
    
class Vampire:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def sound(self):
        print("Wryyyyyyyy!!")
    def time_stop(self):
        print("Za warudo!")

Same!

class Animal:
    def __init__(self, name):
        self.name = name
    def hello(self):
        print(self.name)

class Dog(Animal):
    def __init__(self, name, color):
        super().__init__(name)
        self.color = color
    def sound(self):
        print("Woof")
        
class Cat(Animal):
    def __init__(self, name, weight):
        super().__init__(name)
        self.weight = weight
    
class Vampire(Animal):
    def __init__(self, name, age):
        super().__init__(name)
        self.age = age
    def sound(self):
        print("Wryyyyyyyy!!")
    def time_stop(self):
        print("Za warudo!")
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