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:

1 False
2 2325723198184
3 2325723198464

a1与a2的内存地址不同,a1与a2是不一样的.

 1 class A(object):
 2     
 3     def __init__(self):
 4         self.y=10
 5         self.x=44
 6     x=10
 7     y=12
 8 
 9 
10 class B(A):
11 
12     x=8
13     y=20
14 
15 b=B()
16 print(b.y)
17 print(b.x)

结果:

1 10
2 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:

 1 class Settings(object):
 2     _instance = None
 3 
 4     def __new__(cls, *args, *kw):
 5         if not cls._instance:
 6             cls._instance = super(Settings, cls).__new__(cls, *agrs, **kw)
 7         return cls._instance
 8 
 9 s1 = Settings()
10 s2 = Settings()
11 
12 print(s1 == s2)
13 print(id(s1))
14 print(id(s2))

结果:

1 True
2 1705906981800
3 1705906981800

小彩蛋:

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

结果:

1 True
2 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.