一、class object、class variable
首先class在python里面是一个对象,它有独立区域存储属于自己的数据,而不需要实例化。
class Hehe(object): count = 0 # class variable def __init__(self, c): Hehe.count = Hehe.count + c print 'addres same' if id(Hehe.count) == id(self.count) else 'addres not same' #addres same self.count = self.count + c # instance variable print 'addres same' if id(Hehe.count) == id(self.count) else 'addres not same' #addres not same print 'class var: %d' %Hehe.count print 'instance var: %d' %self.count h1 = Hehe(1) print '' h2 = Hehe(10) 输出: addres same addres not same class var: 1 instance var: 2 addres same addres not same class var: 11 instance var: 21
结论:
- instance 变量未赋值前value为class 变量地址是一样的,赋值后,地址发生变更,这说明class变量与instance变量是两个引用
- instance 变量生存范围在instance层级,class变量生存在class 对象里
二、@classmethod和@staticmethod
class Hehe(object): count = 0 # class variable def __init__(self, c): Hehe.count = Hehe.count + c self.count = self.count + c # instance variable @classmethod def get_class_count(cls_obj): return cls_obj.count @staticmethod def a_static_method(): pass h1 = Hehe(1) # class level print h1.get_class_count() # 11 print h1.count # 2 # instance level print Hehe.get_class_count() # 11 print Hehe.count # 11
结论:
- @classmethod标记的方法可以通过class直接调用,因为第一个参数包含class object,所以可以拿到class variable
- @staticmethod和@classmethod都可以被class直接调用,但@staticmethod拿到不到class object
贴个stackflow的图片:
http://stackoverflow.com/questions/12179271/python-classmethod-and-staticmethod-for-beginner
-end