Some built-in methods of the class

Built-in method

Any type of data will take some more or less the method of bis

Double Down method: __init__ __str__ __xxx__

In each book python species, also known as magic methods built-in methods

Features : not serious, when the call is not always a good call

example:

'abc'.split('b') # 正经调用str类型的split方法

print('abc' + 'efg')  # 直观

ret = 'abc'.__add__('efg')  # 不直观,不正经调用方法
print(ret)

Important way

• __str__

  The default print object is printed is the memory address of the object, but does not address the role defined in the class for me __str__method, return back, equivalent to replace the memory address of the default print object Note : A string must be return back Content

  For example, print (obj) (obj is a target), when, in fact, always invoked obj.__str__(), printing the return value of this method

  Easy to do print (such as class annotation)

  # __str__
  class Course:
  course_lst = []
  def __init__(self,name,period,price):
  self.name = name
  self.period = period
  self.price = price
  def __str__(self):
  return '%s,%s,%s'%(self.name,self.period,self.price)
  # python = Course('python','6 months',19800)
  # linux = Course('linux','5 months',17800)
  # Course.course_lst = [python,linux]
  # for course in Course.course_lst:
  #     print(course)  
  # 打印一个对象总是打印内存地址,这个数据对我们来说没有用
  # 打印这个对象的时候查看这个对象的相关信息

• __new__

  Object instantiation process types, the program first creates a memory address, and then call __init__, we never cared to open up the memory space of things instantiation, because someone did help me, help us open up this memory space that __new__method

  No objects does not matter, we can own a new

  1. Test case

  class A:
      def __new__(cls,*args,**kwargs):
          print('执行我了')    
      def __init__(self):
          print('init')
          self.name = 'alex'
  A()
  
  # 结果
  # 执行我了
  # 默认来说,__new__方法是替我们开辟内存空间,但是我们这里将__new__执行的改为了打印,
  # __init__没有内存空间,也就不会执行了
  
  # new是没有self参数

  # Introduction to Algorithms - microscopic

  # 23 design patterns - Macro