物件導向程式設計基礎

Python 物件導向程式設計進階

Jake Roach

Data Engineer

定義類別

class Person:
  def __init__(self, name, age):
    self.name = name
    self.age = age
    self.height = 0

# This invokes a call to __init__
john = Person("John Casey", 38)

使用 class 關鍵字定義類別
__init__ 稱為建構子，建立新物件時會被呼叫
self 指向目前這個類別的實例

實例屬性

class Person:
  def __init__(self, name, age):
    self.name = name
    self.age = age

# Create an instance of Person
sarah = Person("Sarah Walker", 31)
sarah.age  # Retrieve the age instance attribute

與某個類別物件相關聯
以 self.<attribute-name> 設定與存取
以 <object-name>.<attribute-name> 來取得

類別屬性

隸屬於類別本身
不需建立物件即可存取
儲存所有物件都相同的資料

class Person:
  residence = "Planet Earth"
  ...

# Accessed without an instance
print(Person.residence)

Planet Earth

實例方法

class Person:
  ...
  def introduce(self):
      print(f"Hello, my name is {self.name}")

chuck = Person("Chuck", 32)
chuck.introduce()  # Called on a Person object

需要已有該類別的物件才能呼叫
以 self 為第一個參數

類別方法

class Person:
  @classmethod
  def wake_up(cls):
      print("Time to start your day!")

# Calling a class method
Person.wake_up()

以 @classmethod 修飾
不需類別物件即可呼叫

繼承

繼承可在類別間重複使用程式碼。

子類別（Employee）會繼承父類別（Person）的所有功能
為「is-a」關係
可再加入額外功能
- 屬性
- 方法

class Person:
  def __init__(self, name, age):
    self.name
    self.age = age

  def introduce(self):
      print(f"Hello, my name is {self.name}")

class Employee(Person):
  def __init__(self, name, age, title):
    Person.__init__(self, name, age)
    self.title = title

  def change_position(self, new_title):
      self.title = new_title

繼承

lester = Employee("Lester", 26, "Technician")
lester.introduce()  # Inherited from Person
print(lester.title)

Hello, my name is Lester
Technician

lester.change_position("Cashier")
print(lester.title)

Cashier

super()

class Employee(Person):
  def __init__(self, name, age, title):
    # Uses name of the parent class
    Person.__init__(self, name, age)

    self.title = title
  ...

類別名稱、__init__()

使用 super()

class Employee(Person):
  def __init__(self, name, age, title):
    # super(), instead of class name
    super().__init__(name, age)

    self.title = title
  ...

super()、__init__()
不需傳入 self

覆寫

子類以全新的方式實作從父類繼承的方法。

class Employee(Person):
  ...
  def introduce(self):
      print(f"""My name is {self.name},
        I am a {self.title}""")

lester = Employee("Lester", 26, "Technician")
lester.introduce()

My name is Lester, I am a Technician

多載

class Person:
  def __init__(self, name):
      self.name = name

  def __eq__(self, other):
      return self.name == other.name

為類別自訂 Python 運算子的行為
__eq__() 用來多載 ==

# Compare two Person objects
chuck = Person("Charles Carmichael")
charles = Person("Charles Carmichael")
print(chuck == charles)

True

一起來練習吧！

Python 物件導向程式設計進階