python面向对象的特殊方法补充

特殊方法

• 初始化方法

  • init

• 创建前置方法，在init之前 (构造方法)

  • new

  class practise(object):
      def __init__(self,name):
              self.name = name
      def __new__(cls,*args,**kwagrs)
              print('正在创建新方法')
              return object.__new__(cls) 

• call方法，对象执行(object())加括号，默认执行类下的__ call __ 方法

  class practise(object):
      def __init__(self,name):
              self.name = name
      def __call__s(self,*args,**kwagrs)
              print('正在执行call方法')
      
      
      >>> a = practise('alex')
      >>> a() #正在执行call方法

• str方法 将对象字符串格式化(str(obj)),返回字符串(备注)

  class practise(object):
      def __init__(self,name):
              self.name = name
      def __str__(self):
          return '这是str方法'
  
  a = practise()
  b = str(a)
  print(b)
  
  print(a) #可直接print对象，显示类的备注

• dict方法(展示全部变量从类或者对象)(以字典存在)

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

• setitem getitem delitem (仿dict方法)

  #info的方法
  class info(object):
      def __init__(self,name):
          self.name = name
  
      def __setitem__(self, key, value):
          print(f'{key}:{value}')
  
      def __getitem__(self,name):
          print(f'{name}')
  
      def __delitem__(self,name):
          print(f'del {name}')
  
  a = info('alex')
  a['213'] = 456
  a['123']
  del a['123']

• enter,exit(类似装饰器)

  • with … as …必须拥有enter和exit
  • with … as … f 名称为上下文管理

  #模拟数据库连接
  class connectsql(object):
      def __enter__(self):
          self.sqlconect = link to sql
          return sqlconect
      def __exit__(self, type, value, traceback):
          self.sqlconnect.close()
  
  with connectsql() as f:
          f.操作()
      
  
  #with+类调用
  class longlongago(object):
      def __init__(self,name):
          self.name = name
      def show_name(self):
          print(self.name)
      def __enter__(self):
          return self
      def __exit__(self, type, value, traceback):
          print('结束')
  
  with longlongago('alex') as f:
      f.show_name()

• add

  • 对象相加

  #对象相加
  class plusobj(object):
      def __init__(self,name):
          self.name = name
      def __add__(self,other):
          return self.name + other.name
  
  a = plusobj('aka')
  b = plusobj('cui')
  c = a + b
  print(c)