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  • Python中is和==的区别

    不废话,直接上结论:

    ==  比较操作符:用来比较两个对象是否相等。 (见例1)
    is  同一性运算符:比较两个对象的id值是否相等,即是否是同一对象,是否指向同一个内存地址。(见例2)

     补充:当两个对象值相同时,只有其为数值型或字符串型,a is b才为True,当a和b是tuple,list,dict或set型时,a is b为False 。(见例3)

    详解:

    Python中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)

    例1.

    >>> a = 'cheesezh'
    >>> b = 'cheesezh'
    >>> a == b
    True

    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))
    3075326572
    >>> print(id(y))
    3075326572
    >>> print(id(z))
    3075328140

    例3.

    >>> a = 1 # a和b为数值类型
    >>> b = 1
    >>> a is b
    True
    >>> id(a)
    14318944
    >>> id(b)
    14318944
    >>> a = 'cheesezh' # a和b为字符串类型
    >>> b = 'cheesezh'
    >>> a is b
    True
    >>> id(a)
    42111872
    >>> id(b)
    42111872
    >>> a = (1,2,3) # a和b为元组类型
    >>> b = (1,2,3)
    >>> a is b
    False
    >>> id(a)
    15001280
    >>> id(b)
    14790408
    >>> a = [1,2,3] # a和b为list类型
    >>> b = [1,2,3]
    >>> a is b
    False
    >>> id(a)
    42091624
    >>> id(b)
    42082016
    >>> a = {'cheese':1,'zh':2} # a和b为dict类型
    >>> b = {'cheese':1,'zh':2}
    >>> a is b
    False
    >>> id(a)
    42101616
    >>> id(b)
    42098736
    >>> a = set([1,2,3])# a和b为set类型
    >>> b = set([1,2,3])
    >>> a is b
    False
    >>> id(a)
    14819976
    >>> id(b)
    14822256

     

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  • 原文地址:https://www.cnblogs.com/liangmingshen/p/11646349.html
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