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比较两个变量是否在python中引用了同一对象

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问题：比较两个变量是否在python中引用了同一对象
回答 0
回答 1
回答 2
回答 3
回答 4
回答 5

问题：比较两个变量是否在python中引用了同一对象

如何检查两个变量是否引用同一对象？

x = ['a', 'b', 'c']
y = x                 # x and y reference the same object
z = ['a', 'b', 'c']   # x and z reference different objects
点击查看英文原文

How to check whether two variables reference the same object?

x = ['a', 'b', 'c']
y = x                 # x and y reference the same object
z = ['a', 'b', 'c']   # x and z reference different objects

回答 0

就是这样is：x is y返回Trueif x和y是否为同一对象。

点击查看英文原文

That’s what is is for: x is y returns True if x and y are the same object.

回答 1

y is x会True，y is z会False。

点击查看英文原文

y is x will be True, y is z will be False.

回答 2

虽然两个正确的解决方案x is z，并id(x) == id(z)已经公布，我想指出的Python的实现细节。Python将整数存储为对象，作为一种优化，Python会在其开始处生成一堆小整数（-5到256），并将每个具有小整数的变量指向每个预初始化的对象。更多信息

这意味着对于初始化为相同小数（-5到256）的整数对象，检查两个对象是否相同将返回true（就我所知这是一个实现细节，在ON C-Pyhon上），而对于较大的对象数字，仅当一个对象从另一个对象初始化时，它才返回true。

> i = 13
> j = 13
> i is j
True

> a = 280
> b = 280
> a is b
False

> a = b
> a
280
> a is b
True
点击查看英文原文

While the two correct solutions x is z and id(x) == id(z) have already been posted, I want to point out an implementation detail of python. Python stores integers as objects, as an optimization it generates a bunch of small integers at its start (-5 to 256) and points EVERY variable holding an integer with a small value to these preinitialized objects. More Info

This means that for integer objects initialized to the same small numbers (-5 to 256) checking if two objects are the same will return true (ON C-Pyhon, as far as I am aware this is an implementation detail), while for larger numbers this only returns true if one object is initialized form the other.

> i = 13
> j = 13
> i is j
True

> a = 280
> b = 280
> a is b
False

> a = b
> a
280
> a is b
True

回答 3

您还可以使用id（）来检查每个变量名称所引用的唯一对象。

In [1]: x1, x2 = 'foo', 'foo'

In [2]: x1 == x2
Out[2]: True

In [3]: id(x1), id(x2)
Out[3]: (4509849040, 4509849040)

In [4]: x2 = 'foobar'[0:3]

In [5]: x2
Out[5]: 'foo'

In [6]: x1 == x2
Out[6]: True

In [7]: x1 is x2
Out[7]: False

In [8]: id(x1), id(x2)
Out[8]: (4509849040, 4526514944)
点击查看英文原文

You can also use id() to check which unique object each variable name refers to.

In [1]: x1, x2 = 'foo', 'foo'

In [2]: x1 == x2
Out[2]: True

In [3]: id(x1), id(x2)
Out[3]: (4509849040, 4509849040)

In [4]: x2 = 'foobar'[0:3]

In [5]: x2
Out[5]: 'foo'

In [6]: x1 == x2
Out[6]: True

In [7]: x1 is x2
Out[7]: False

In [8]: id(x1), id(x2)
Out[8]: (4509849040, 4526514944)

回答 4

我真的很想收到视觉反馈，这就是为什么有时我只打开http://www.pythontutor.com/visualize.html#mode=edit来查看内存分配方式以及引用什么的原因。

添加了这个很棒的gif，因为此回复是关于可视化的。

点击查看英文原文

I really like to have a visual feedback, that’s why I sometimes just open up http://www.pythontutor.com/visualize.html#mode=edit to see how the memory is allocated and what is referencing what.

Added this awesome gif as this reply is about visualizing..

回答 5

这来自docs.python.org：“每个对象都有一个标识，一个类型和一个值。创建后，对象的标识就永远不会改变；您可以将其视为对象在内存中的地址。“ is”运算符比较两个对象的标识； id（）函数返回一个表示其标识的整数。”

显然，每次更改值时，都会根据标识更改指示重新创建对象。x = 3行，后跟x = 3.14行，没有错误，并且为x提供了不同的标识，类型和值。

点击查看英文原文

This is from docs.python.org: “Every object has an identity, a type and a value. An object’s identity never changes once it has been created; you may think of it as the object’s address in memory. The ‘is’ operator compares the identity of two objects; the id() function returns an integer representing its identity.”

Apparently every time you change the value the object is recreated as indicated by the identity changing. The line x=3 followed by the line x=3.14 gives no error & gives different identities, types and values for x.