093 reflection

First, what is reflected

It is reflected to the operation by the object class or string property

Is acquired by a string, setting, deleting object property or method

Second, how to use reflection

• Essentially reflected in the use of built-in functions, wherein the reflector has four built-in functions:

1. hasattr: determining whether there is a method of the class
2. getattr: to acquire memory address corresponding to the method according to the string in the object obj, added "()" to perform the brackets
3. setattr: setattr the outside by a function bound to the instance
4. delattr: Delete a class or instance method

class Foo:
    def __init__(self,name,pwd):
        self.name = name
        self.pwd = pwd

    def run(self):
        print('run')
    def speak(self):
        print('speak')

p=Foo('xichen',18)

• hasattr: determining whether there is a method of the class

  print(hasattr(p,'name'))

  True

• getattr: to acquire memory address corresponding to the method according to the string in the object obj, added "()" to perform the brackets

  if hasattr(p,cmd):
      run=getattr(p,cmd)
      run()
  else:
      print('该命令不存在')

  Please enter the command: run

  run

• setattr: setattr the outside by a function bound to the instance

  1.通过用户输入将外部的属性添加到当前的实例中
  print(p.__dict__)
  key=input('请输入key:')
  value=input('输入value:')
  setattr(p,key,value)
  print(p.__dict__)

  { 'name': 'xichen' , 'pwd': 18}
  Enter key: age
  input value: 18 is
  { 'name': 'xichen', 'pwd': 18 is, 'Age': '18 is'}

  2.动态的将外部的方法添加到当前的实例中
  def test(a):
      print(a)
  
  print(p.__dict__)
  setattr(p,'test',test)
  print(p.__dict__)
  
  p.test(0)

  {'name': 'xichen', 'pwd': 18}
  {'name': 'xichen', 'pwd': 18, 'test': <function test at 0x000001D1E98069D8>}
  0

• delattr: Delete a class or instance method

  1.最原始的删除对象的属性方法
  print(p.__dict__)
  del p.name
  print(p.__dict__)

  {'name': 'xichen', 'pwd': 18}
  {'pwd': 18}

  2.动态删除p中属性为变量a的属性
  a=input('请输入要删除的属性:')
  print(p.__dict__)
  delattr(p,a)
  print(p.__dict__)

  Enter the property to delete: pwd # Remove object attributes are attributes pwd string
  { 'name': 'xichen', 'pwd': 18 is}
  { 'name': 'xichen'}

Third, an example of using reflection

1. Determine what object there is no property that I entered, and if so, print

   cmd=input('请输入要查询的属性:')
   if hasattr(p,cmd):
       a=getattr(p,cmd)
       print(a)
   else:
       print('该属性不存在')

   Please enter a query attributes: name
   xichen