Python 对象包含的三个基本要素,分别是: id(身份标识),type(数据类型)和value(值)
is 和 == 都是等值判断的.但对对象等值判断的内容并并不相同
== 用来比较两个对象的 value 值是否相同is 用来比较两个对象的 id 是否相同
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| >>> a = 1
>>> b = 1
>>> a is b
True
>>> a = 1.2
>>> b = 1.2
>>> a is b
False
>>> a = 257
>>> b = 257
>>> a is b
False
>>> a = 'hello'
>>> b = 'hello'
>>> a is b
True
>>> a = 'hello world'
>>> b = 'hello workd'
>>> a is b
False
>>> a = (1,2,3)
>>> b = (1,2,3)
>>> a is b
False
>>> a = [1,2,3]
>>> b = [1,2,3]
>>> a is b
False
>>> a = {'cheese':1,'zh':2}
>>> b = {'cheese':1,'zh':2}
>>> a is b
False
>>> a = set([1,2,3])
>>> b = set([1,2,3])
>>> a is b
False
|
如上示例中,当 a,b 值为 [-5,257) 的整数值时,会返回 True.其原因是 Python 为了优化速度,内部维护了小整数对象池,避免整数频繁申请和销毁内存空间.此值的区间为 [-5, 257).
同样的,对于字符串也有一个类似的对象池.但尚不了解字符串长度范围.
