Python Learning notes 009_ construction and destruction

>>> # Magic Method
>>>
>>> # Magic methods are always surrounded by double underscores , such as __init__
>>> # Magic method is all about object-oriented Python
>>> # The Magic of magical methods is reflected in their ability to be automatically invoked at the right time
>>>

>>> # __init__ (self[,...]) is equivalent to other language constructs, which are automatically invoked when a class object is instantiated
>>> # The return value of the __init__ method is none, never write return

 >>> class   Rectangle:  Span style= "color: #0000ff;" >def  __init__   (Self,x,y): self.x  = x self.y  = y  def  Getperi (self): #   Get the perimeter of the rectangle  
   
    return  (self.x + self.y) * 2 
    def  
     Getarea ( Self):  
    return  self.x *
     Self.y  ;>> rect = Rectangle (3,4
    )  >>>
     14>>> Rect.getarea ()  12>>> 
   

>>> # __init__ () method is not the first method called, but __new__ (cls[,...])
>>>
>>> # __new__ method, we usually seldom go to rewrite it
>>>
>>> # There is a situation where you need to rewrite the __new__ method, which is when you inherit an immutable class and you need to modify it
>>>

class capstr (str):      def__new__(cls,string):        string=string.upper ()        return str.__new__(cls,string)    >>> a = Capstr ("I Love you!< /c15>")>>> a'I Love you! '>>>

>>> # If the __init__ method and the __new__ method are constructors, then the __del__ method is the destructor method
>>> # The __del__ (self) method is automatically called when the object is to be destroyed, which is used when the garbage collection mechanism
>>>

The >>> # __del__ method does not mean that we execute del obj and will be called, but all references to it will be called after Del.

>>>classC:def __init__(self):Print("I am the __init__ method, I was called ...")    def __del__(self):Print("I am the __del__ method, I was called ...")        >>> C =C () I am the __init__ method, I was called ...>>> C2 =C>>>delC>>>delC2 I was the __del__ method, I was called ...

Python Learning notes 009_ construction and destruction