01.python对象

# 11是个int型对象
>>> type(11)
<type ‘int‘>

# 类型对象的类型是type，所有类型对象的类型都是type，它是所有python类型的根和所有python标准类的默认元类
>>> type(type(11))
<type ‘type‘>

class NonTest:
    #  __nonzero__必须是静态的  
    @staticmethod
    def __nonzero__(self):
        pass


if __name__ == ‘__main__‘:
    if NonTest():
　　　　 print(True) # True 

class NonTest:
    def __len__(self):
        return 0


class NonTest2:
    def __len__(self):
        return 1


if __name__ == ‘__main__‘:
    if NonTest():
        print(‘NonTest‘)
    if NonTest2():
        print(‘NonTest2‘)  # 打印 NonTest2

# python3.7测试
if __name__ == ‘__main__‘:
    # foo1 和 foo2 指向相同的对象
    foo1 = foo2 = 4.2
    print(foo1 is foo2)  # True
    # foo3 和 foo4 指向相同的对象
    foo3 = 5.3
    foo4 = foo3
    print(foo3 is foo4)  # True
    # foo5 和 foo6 指向相同的对象
    foo5 = 6.99
    foo6 = 6.99
    print(foo5 is foo6)  # False
    print(id(foo5) == id(foo6))  # foo5 is foo6等价与id(foo5) == id(foo6) # True

#python2.7.10测试 
>>> a = 1.99
>>> id(a)
140195765685264
>>> b = 1.99
>>> id(b)
140195765685240
>>> c = 1.99
>>> id(c)
140195765685216
>>> 

# python2中的比较
>>> cmp(a,b)
0
>>> cmp(1,1)
0
>>> cmp(1,2)
-1
>>> cmp(2,1)
1

import operator

if __name__ == ‘__main__‘:
    obj1 = 12.99
    obj2 = 11.99+1.00
    print(operator.eq(obj1, obj2))  # True

# python3不支持
`obj`
# 返回一个对象的字符串表示
repr(obj)

    # isinstance(_o,_t)判断对象类型
    print(isinstance(6, (int, float)))  # True
    print(isinstance(6.1, (int, float)))  # True
    print(isinstance("6.1", (int, float)))  # False
    print(isinstance("6.1", str))  # True