从Python对象三要素来看is和==的区别
Python对象三要素
Python对象包含三个基本要素id,type和value：
| 要素 | 说明 | 获取方式 |
|---|---|---|
| id | 身份标识，基本就是内存地址 | id(obj) |
| type | 数据类型 | type(obj) |
| value | 值 |
is和==的区别
| 标识 | 名称 | 判断因素 |
|---|---|---|
| is | 同一性运算符 | id |
| == | 比较运算符 | value |
举例
例1
a = {"a":1, "b":2}
b = a.copy()
a == b # True value一样
a is b # False id不一样- 1
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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)- 1
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例3
>>> 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)- 1
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通过例3可看出，只有数值型和字符串型的情况下，a is b才为True，当a和b是tuple，list，dict或set型时，a is b为False。