Python object-oriented high-order

__slots__ restricting instances to add extra attributes

To achieve the limit, Python allows you to define a special __slots__ variable to limit the attributes that the class instance can add when defining class:

class Student (object):         __slots__ = ('name','age')   #

Use __slots__ to note that __slots__-defined properties do not work on inherited subclasses only for the current class instance

class graduatestudent (Student):         Pass  =#  inherited subclasses can implement modifications # unless __slots__ is also defined in a subclass, so that the subclass instance allows the defined property to be its own __slots__ Add the __slots__ of the parent class. 

@property

Python's built-in @property decorator is responsible for turning a method into a property call

class :     def __init__ (self,name,width,length):        self.name=name        self.width=width        self.length= length    @property    def area (self):        return self.width * self.lengthr1=room ('Alex', ' a ')print(R1.area)

Custom class Python's class has a lot of special later Han books to help us customize our class.

__str__ __repr__

# define a student class to print an instance class Student (object):         def __init__ (self, name):                 = nameprint(Student ('micheal'))
<__main__. Student object at 0x00000000028d1128>  #__str__ method is to make this line clearer

Commonly used __str__ __repr__ usage is to combine them with

class Student (object):     def __init__ (self, name):         = name    def__str__(self):        return'  Student object (name=%s)' % self.name    __repr____str__

The "' str ' function or the print function--->obj.__str__ () repr or the interactive interpreter--->obj.__repr__ () if __str__ is not defined, then __repr__ is used instead of the output note: The return value of both methods must be a string, otherwise throw an exception "'

Python-style getter setters are also implemented in the property

Class Foo:        @property:        def aaa (self):                print (' Get with this ')        @AAA. Setter        def aaa (self , value):                print (' Set with this ') #只有在属性AAA定义property后才能定义AAA. Setterf1 = Foo () F1. AAA # call GETF1. Aaa= ' AAAASD1 ' #调用 set     

Another form of implementation is __getattr__ __setattr__ ()

classfoo:x=1def __init__(self,y): Self.y=ydef __getattr__(self, item):Print('----> from getattr: The attribute you are looking for does not exist')    def __setattr__(self, Key, value):Print('----> from setattr')        #Self.key=value #这就无限递归了, you think about it.        #Self.__dict__[key]=value #应该使用它#__setattr__ Adding/Modifying a property will trigger its executionF1=foo (10)Print(F1.__dict__)#because you rewrite the __setattr__, any assignment operation will trigger its operation, you do not write anything, is not assigned at all, unless you directly manipulate the property dictionary, otherwise you can never assign a valueF1.z=3Print(F1.__dict__)#__getattr__ fires only when a property is called with a point and the property does not existF1.xxxxxx

__call__ when we invoke an instance method, we may use the isinstance (obj) call or use the __call__ method.

Use of enumeration classes

 from Import Enum class Gender (Enum):     = 0    = 1class  Student (object):    def__init__(self, Name, gender):        = name        == Student ('Bart', Gender.male)

The contents of the meta-class are vaguely understood. Read through the Liaoche of the teacher's meta-class introduction

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Python object-oriented high-order