面向对象编程（python）

面向对象编程

self

• 类方法与普通函数只有一种特定的区别----前者必须有一个额外的名字，这个名字必须添加到参数列表的开头，但是你不用再调用这个功能时为这个参数赋值

• 按照惯例，它被赋予self这一名称

• Sample Code：

    class Person:
    def say_hi(self):
        print('say hi!!!');
    p = Person();
    p.say_hi();
  

init方法

• 会在类的对象被实例化时立即执行
• Sample Code：

    class Person:
        def __init__(self,name):
            self.name = name;
        def say_hi(self):
            print('say hi!!! to',self.name);
    p = Person("endian11");
    p.say_hi();

类变量与对象变量

• 数据部分也就是字段，只不过是绑定到类与对象的命名空间。这就代表着这些名称仅在这些类与对象所存在的上下文中有效

• 字段有两种类型

  • 类变量
    • 类变量是共享的，它可以被属于该类的所有实例访问
  • 对象变量
    • 由类的每一个独立的对象或实例所拥有

• Sample Code

  class Robert:
      """表示有个带有名字的机器人."""
      population = 0;#一个类变量，用来计数机器人的数量
      def __init__(self,name):
          '''初始化数据'''
          self.name = name;
          print("(Initializing {})".format(self.name));
          Robert.population +=1;
      def die(self):
          '''我挂了。。'''
          print('{} is beging destroyed!'.format(self.name));
          Robert.population -=1;
          if Robert.population ==0:
              print('{} was the last one.'.format(self.name));
          else:
              print("There are still {:d} roberts working.".format(Robert.population));
      def say_hi(self):
          '''来自机器人的诚挚问候
          
          没问题，你做的到。'''
          print("Greetings, my masters call me {}.".format(self.name));
      @classmethod
      def how_many(cls):
          '''打印出当前的人口数量'''
          print("We have {:d} robots.".format(cls.population));
          
  droid1 = Robert("R2-D2");
  print(droid1.__init__.__doc__);
  droid1.say_hi();
  Robert.how_many();
  droid2 = Robert("c-3P0");
  droid2.say_hi();
  Robert.how_many();
  print("\nRobots can do some work here.\n");
  print("Robots have finished their work,so let us  destroy them");
  droid1.die();
  droid2.die();
  Robert.how_many();
  

  • 运行结果：

      (Initializing R2-D2)
      初始化数据
      Greetings, my masters call me R2-D2.
      We have 1 robots.
      (Initializing c-3P0)
      Greetings, my masters call me c-3P0.
      We have 2 robots.
      
      Robots can do some work here.
      
      Robots have finished their work,so let us  destroy them
      R2-D2 is beging destroyed!
      There are still 1 roberts working.
      c-3P0 is beging destroyed!
      c-3P0 was the last one.
      We have 0 robots.
    

继承

• 面向对象编程的一大优点是对代码的重用

• SampleCode：

    class SchoolMember:
    '''代表学校里的成员。'''
    def __init__(self,name,age):
        self.name = name;
        self.age = age;
        print('(Initialized SchoolMember:{})'.format(self.name));
    def tell(self):
        '''告诉我有关我的细节。'''
        print('Name:"{}" Age:"{}"'.format(self.name,self.age),end=" ");
    class Teacher(SchoolMember):
        '''代表一位老师。'''
        def __init__(self,name,age,salary):
            SchoolMember.__init__(self,name,age);
            self.salary = salary;
            print('Initialized Teacher:{}'.format(self.name));
        def tell(self):
            SchoolMember.tell(self);
            print('Salary {:d}:'.format(self.salary));
            
    class Student(SchoolMember):
        def __init__(self,name,age,marks):
            SchoolMember.__init__(self,name,age);
            self.marks = marks;
            print('Initialized Student:{}'.format(self.name));
        def tell(self):
            SchoolMember.tell(self);
            print('Marks:"{:d}"'.format(self.marks));
    
    t = Teacher("Li Zhanwei",28,25000);
    s = Student("Li Xiaolong",22,66);
    t.tell();
    s.tell();
    
    print();
    
    members = {t,s};
    for m in members:
        m.tell();
  

  • 如果基类和子类都有相同的方法，python代码不会自动调用基类的函数，需要自己显式地调用