Python basic tutorial: define a class to create an instance

class definition

In Python, classes are defined by the class keyword, and the class name starts with a capital letter

>>>class Person(object):           #所有的类都是从object类继承
              pass                 #pass先不做任何处理，先跳过，为了防止语法错误

Create class properties

>>> class Person(object):
         address = 'Earth' #类的属性直接在类内部定义,当实例属性和类属性重名时，实例属性优先级高
         def __init__(self, name):
                self.name = name
>>> Person.address          #直接通过类.属性可以访问
'Earth'
>>>p1=Person('A')                               
>>>p1.address               #通过创建类的实例，也可以通过实例.属性访问
'Earth'
>>> Person.address='KKKK'   #类的属性可以动态修改
>>> Person.address
'KKKK'
>>>p1.address               #类的属性一经修改，所有访问的属性值也随之更改
'KKKK'

instance creation

To create an instance, use the class name + (), which is similar to a function call:

E.g:

>>> class Person(object):
             pass
 
>>> p1 = Person()                      #创建实例
>>> p1.name = 'Bart'                   #创建实例属性
>>> p2 = Person()
>>> p2.name = 'Adam'

Initialize instance properties

>>> class Person(object):
             class=1                           #定义类属性
             def __init__(self, name,age):         
 #__init__(self,属性1，属性2....)：self代表实例，通过self访问实例对象的变量和函数
             self.name = name
             self.__age=age                                        
#实例的私有属性无法从外部访问，但是，从类的内部是可以访问的
#定义实例方法
             def get_name(self):
                   return self.__age                              
#实例方法，定义在类内部，可以访问实例的私有属性__age
#定义类方法
             @classmethod
             def how_many(cls):                                   
#通过@classmethod标记类方法，类方法的第一个参数为cls，cls.class相当于Person.class
                  return cls.class                                
#类方法中无法调用任何实例的变量，只能获得类引用
>>> p1 = Person('Bob',12)
>>> print (p1.get_age())                                          

Notice:

The difference between underscore and double underscore:

Starting with a single underscore _foo represents a class attribute that cannot be directly accessed. It needs to be accessed through the interface provided by the class. Then the name starting with _ will not be imported, that is, it cannot be imported with from xxx import *, unless the module or package The __all__ list in contains them explicitly;

__foo starting with a double underscore represents a private member of the class, which can only be accessed by the class itself, and its subclass objects cannot access this data either.