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.