Python_面向对象_单例模式

class A(object):
    pass

a1 = A()
a2 = A()

print(a1 == a2)
print(id(a1))
print(id(a2))

结果:

 False
 2325723198184
 2325723198464

a1与a2的内存地址不同,a1与a2是不一样的.

 class A(object):

     def __init__(self):
         self.y=10
         self.x=44
     x=10
     y=12

 class B(A):

     x=8
     y=20

 b=B()
 print(b.y)
 print(b.x)

结果:

 10
 44

程序执行过程:

　　先找def的值,然后找class中其他的,找不到再去父类中去找,知道后就停止向上级查找,输出结果.

单例模式:

 class Settings(object):
     _instance = None

     def __new__(cls, *args, *kw):
         if not cls._instance:
             cls._instance = super(Settings, cls).__new__(cls, *agrs, **kw)
         return cls._instance

 s1 = Settings()
 s2 = Settings()

 print(s1 == s2)
 print(id(s1))
 print(id(s2))

结果:

 True
 1705906981800
 1705906981800

小彩蛋:

 print(1<2==2)
 print(1 < 2 and 2 == 2)

结果:

 True
 True

按照该官方文档解释，

”5== len(a)== len(b)“等价于”5== len(a) and len(a)==len(b)“

以此类推,得到上述结果.