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Python class類別的使用

Sharon Peng
14 min readJun 8, 2021

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話不多說，直接進入重點。

Outline:

  • 定義Class類別
  • 在類別中的使用函數(Method)
  • 類別中定義「屬性」(Property)
  • 在類別(Method)中又呼叫其他類別(Method)
  • 設定類別(Method)與屬性(Property)的私有與公開
  • 繼承（重要！！）
  • 多重繼承
  • 呼叫父類別的函式(Method)或屬性(Property)

＊定義Class類別

class FirstClass(object):   # 繼承 python最上層的object類別
      def __init__(self):   # 稱為 constuctor，建構方法
            print("hello")hi = FirstClass()    # 建立一個名為hi的類別--------------------------------------------------------------------Output:
hello

建構方法是甚麼呢？

在Java中也可以看到類似的概念，其實就是在建立一個物件的時候，要給他一個初始的狀態。而建構方法，是來完成這項任務的手段。

另一種初始化的方式，「自訂初始化的值」。

class FirstClass(object):
    def __init__(self, name):  # constructor
        print("hello " + str(name))


hi = MyClass('Jack') # 建立一個名為hi的類別，並傳入參數--------------------------------------------------------------------Output:
hello Jack

＊在類別中的使用函數(Method)

class FirstClass(object):
    def __init__(self, name):
        print("hello " + str(name))

    def fun1(self):                   # 定義一個名為fun1的函式
        print("This is function1")    # 定義一個名為fun2的函式，因為後面有多宣告，代表此函式可以傳入參數
    def fun2(self, num1 = 0, num2=0):
        return (num1 * 2) + num2
hi = MyClass('Jack')
hi.fun1()
print(hi.fun2(1, 2))   # 傳入1, 2參數進去
# print(hi.fun2(1, 2))== print(hi.fun2(num1=1, num2=2))--------------------------------------------------------------------Output:
hello Jack
This is function1
4

如果再fun2裡面不傳參數的話，則會默認那個數值是一開始預設的num1=0, num2=0。

＊注意！！

函式(def)的第一個參數必須加上self，表示說我是使用目前的物件。(如果不是很懂沒關係，看之後的範例應該就可以理解它的功用了)

＊類別中的「屬性」(Property)

屬性描述此物件的性質。以下方為例，類別為People，描述「人」這項類別有哪些特徵，身高體重等等。

class People(object):
    height = 150  # Property
    weight = 50   # Property

    def __init__(self, h, w):
        self.height = h
        self.weight = w

    def BMI(self):
        bmi = self.weight / (self.height / 100)**2
        print(bmi)


bill = People(170, 60)
bill.BMI()
print(bill.height)
print(bill.weight)--------------------------------------------------------------------Output:
20.761245674740486
170
60

Note:

def __init__(self, h, w):
        self.height = h
        self.weight = w# 這邊我們不是直接把height = h, weight = w，而是用self.height = h，在這邊的self就代表說，我們是用某個建立好的物件將他的，某某.height = h。

＊在類別(Method)中又呼叫其他類別(Method)

class People(object):
    height = 150
    weight = 50
    name = 'unknown'

    def __init__(self, h, w, n):
        self.height = h
        self.weight = w
        self.name = str(n)

    def BMI(self):
        bmi = self.weight / (self.height / 100)**2
        self.Print(bmi)   # 在這邊直接呼叫下面的Print函式

    def Print(self, num):
        print(str(self.name) + "\nheight: " + str(self.height) + "\nweight: " + str(self.weight))
        print("His BMI is " + str(num))


bill = People(170, 60, 'bill')
bill.BMI()--------------------------------------------------------------------Output:
20.761245674740486
170
60

＊設定類別(Method)與屬性(Property)的私有與公開

這邊的私有與公開(在C++中，稱為private, public)，代表外界不能隨意地修改，或是去使用它。如果硬去訪問它的話會出現error，請看下面範例。

class People(object):
    height = 150
    weight = 50
    __name = 'unknown'

    def __init__(self, h, w, n):
        self.height = h
        self.weight = w
        self.__name = str(n)  # 設定私有屬性

    def __BMI(self):          # 設定私有函式(Method)
        bmi = self.weight / (self.height / 100)**2
        print(bmi)

    def printHeight(self):
        print(self.height)

    def printWeight(self):
        print(self.weight)

    def __printName(self):
        print(self.__name)


bill = People(170, 60, 'bill')--------------------------------------------------------------------bill.BMI()    
--------------------------------------------------------------------Output: AttributeError: 'People' object has no attribute 'BMI'
訪問到不該訪問的類別
----------------------------------------------------------------------------------------------------------------------------------------bill.name()
--------------------------------------------------------------------Output: AttributeError: 'People' object has no attribute 'name'
訪問到不該訪問的類別--------------------------------------------------------------------bill.printHeight()
bill.printWeight()
--------------------------------------------------------------------Output:
170
60

＊繼承

這邊來舉一個比較現實的範例，用財產來舉例。爸爸身價有多少，兒子一出生就有多少財產。

class Father(object):
    netWorth = 10**6
    house = 10
    company = 2
    name = 'unknown'

    def __init__(self, m, h, c, n):
        self.money = m
        self.house = h
        self.company = c
        self.name = str(n)

    def printNetWorth(self):
        print("Net Worth: " + str(self.netWorth))

    def printHouse(self):
        print("House Number: " + str(self.house))

    def printComany(self):
        print("Company Number: " + str(self.company))

class Child(Father):  # 這邊原本放的是object，現在改為要繼承的class
    def __init__(self, name):
        print("Child: ", str(name))


bill = Child('bill')  # 這邊建立的是兒子的物件
bill.printNetWorth()  # 兒子此物件的身價可以直接拿爸爸的來使用
bill.printHouse()     # 兒子此物件的房產可以直接拿爸爸的來使用--------------------------------------------------------------------Output:
Child:  bill
Net Worth: 1000000
House Number: 10

＊多重繼承

沒想到的是，bill深藏不露，媽媽居然也是個超級有錢人，身價甚至比爸爸還要高。小孩可以繼承的更多財產了。

class Father(object):
    DadNetWorth = 10**6
    DadHouse = 10
    DadCompany = 2
    DadName = 'Bear'

    def __init__(self,n):
        self.DadName = str(n)

    def printNetWorthFromDad(self):
        print("Dad Net Worth: " + str(self.DadNetWorth))

    def printHouseFromDad(self):
        print("Dad House Number: " + str(self.DadHouse))

    def printComanyFromDad(self):
        print("Dad Company Number: " + str(self.DadCompany))

class Mother(object):
    MomNetWorth = 10 ** 9
    MomHouse = 20
    MomCompany = 10
    MomName = 'Anna'

    def __init__(self, n):
        self.MomName = str(n)

    def printNetWorthFromMom(self):
        print("Mom Net Worth: " + str(self.MomNetWorth))

    def printHouseFromMom(self):
        print("Mom House Number: " + str(self.MomHouse))

    def printComanyFromMom(self):
        print("Mom Company Number: " + str(self.MomCompany))


class Child(Father, Mother):  # 這邊原本放的是object，現在改為要繼承的class
    def __init__(self, name):
        print("Child: ", str(name))

    def func(self):
        super(Child, self).printComanyFromMom()
        super(Child, self).printComanyFromDad()

    def DadandMom(self):
        print("His father is " + super(Child, self).DadName)
        print("His Mother is " + super(Child, self).MomName)


bill = Child('bill')
bill.DadandMom()
bill.func()


bill = Child('bill')
bill.printNetWorthFromDad()
bill.printNetWorthFromMom()
bill.printComanyFromDad()
bill.printComanyFromMom()--------------------------------------------------------------------Output:
Child:  bill
Dad Net Worth: 1000000
Mom Net Worth: 1000000000
Dad Company Number: 2
Mom Company Number: 10

＊呼叫父類別的函式(Method)與屬性(Property)

super(自己類別的名稱, self).要呼叫的「類別」 或 「屬性」)

class Father(object):
    DadNetWorth = 10**6
    DadHouse = 10
    DadCompany = 2
    DadName = 'Bear'

    def __init__(self,n):
        self.DadName = str(n)

    def printNetWorthFromDad(self):
        print("Dad Net Worth: " + str(self.DadNetWorth))

    def printHouseFromDad(self):
        print("Dad House Number: " + str(self.DadHouse))

    def printComanyFromDad(self):
        print("Dad Company Number: " + str(self.DadCompany))

class Mother(object):
    MomNetWorth = 10 ** 9
    MomHouse = 20
    MomCompany = 10
    MomName = 'Anna'

    def __init__(self, n):
        self.MomName = str(n)

    def printNetWorthFromMom(self):
        print("Mom Net Worth: " + str(self.MomNetWorth))

    def printHouseFromMom(self):
        print("Mom House Number: " + str(self.MomHouse))

    def printComanyFromMom(self):
        print("Mom Company Number: " + str(self.MomCompany))


class Child(Father, Mother):  # 這邊原本放的是object，現在改為要繼承的class
    def __init__(self, name):
        print("Child: ", str(name))

    def func(self):
        super(Child, self).printComanyFromMom()  # !!重點!!
        super(Child, self).printComanyFromDad()  # !!重點!!

    def DadandMom(self):
        print("His father is " + super(Child, self).DadName)#!!重點!!
        print("His Mother is " + super(Child, self).MomName)#!!重點!!


bill = Child('bill')
bill.DadandMom()
bill.func()--------------------------------------------------------------------Output:
Child:  bill
His father is Bear
His Mother is Anna
Mom Company Number: 10
Dad Company Number: 2

希望能為各位有所幫助，那我們就下次見吧~~

Python
Class

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Sharon Peng
Sharon Peng

Written by Sharon Peng

508 Followers
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wenhsuanpeng.com 一起精進程式能力吧！！

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