面向对象编程基础

Python 面向对象编程进阶

Jake Roach

Data Engineer

定义类

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 关键字定义类
__init__ 是构造函数，在创建新对象时调用
self 指向类的当前实例

实例属性

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

与类的对象关联
使用 self.<attribute-name> 设置和获取
通过 <object-name>.<attribute-name> 访问

类属性

绑定到类本身
可在没有类实例时获取
存储所有对象应相同的数据

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

# Accessed without an instance
print(Person.residence)

Planet Earth

实例方法

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

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

需要先有类对象才能调用
第一个参数为 self

类方法

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

# Calling a class method
Person.wake_up()

用 @classmethod 装饰
调用时不需要类实例

继承

继承用于在类之间复用代码

子类（Employee）继承父类（Person）的全部功能
"is-a" 关系
可实现额外功能
- 属性
- 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

继承

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
  ...

类名，__init__()

使用 super()

class Employee(Person):
  def __init__(self, name, age, title):
    # super()，而非类名
    super().__init__(name, age)

    self.title = title
  ...

super()，__init__()
不需要传入 self

重写（Overriding）

子类以新的方式实现从父类继承的方法

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

重载（Overloading）

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

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

为类自定义 Python 运算符的行为
__eq__() 用于重载 ==

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

True

Passons à la pratique !

Python 面向对象编程进阶