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python3 is和==的区别

admin 1月 28, 2021 0

Python 对象三要素

要理解Python中is和==的区别，首先要理解Python对象的三个要素:

要素	说明	获取方式
id	身份标识，基本就是内存地址，用来唯一标识一个对象	id(obj)
type	数据类型	type(obj)
value	值	:—–:

is和==区别

标识	名称	判断方法
is	同一性运算符	id
==	比较运算符	value

程序举例

例1：

a = {"a":1, "b":2}
b = a.copy()


a == b  
a is b  # False id不一样

例2：

x = y = [4,5,6]
z = [4,5,6]
x == y
True
x == z
True
x is y
True
>>> x is z
False
>>>
>>> print id(x)
>>> print id(y)
>>> print id(z)

>>> a = 1 #a和b为数值类型
>>> b = 1
>>> a is b
True
>>> id(a)
>>> id(b)
>>> a = 'cheesezh' #a和b为字符串类型
>>> b = 'cheesezh'
>>> a is b
True
>>> id(a)
>>> id(b)
>>> a = (1,2,3) #a和b为元组类型
>>> b = (1,2,3)
>>> a is b
False
>>> id(a)
>>> id(b)
>>> a = [1,2,3] #a和b为list类型
>>> b = [1,2,3]
>>> a is b
False
>>> id(a)
>>> id(b)
>>> a = {'cheese':1,'zh':2} #a和b为dict类型
>>> b = {'cheese':1,'zh':2}
>>> a is b
False
>>> id(a)
>>> id(b)
>>> a = set([1,2,3])#a和b为set类型
>>> b = set([1,2,3])
>>> a is b
False
>>> id(a)
>>> id(b)