为什么Python中没有元组理解？

小灰灰 2022-11-26 07:55 217阅读 0赞

本文翻译自：[Why is there no tuple comprehension in Python?][Why is there no tuple comprehension in Python]

*As we all know, there's list comprehension, like* **众所周知，列表理解**

[i for i in [1, 2, 3, 4]]

*and there is dictionary comprehension, like* **并且有字典理解，例如**

{i:j for i, j in {1: 'a', 2: 'b'}.items()}

*but* **但**

(i for i in (1, 2, 3))

*will end up in a generator, not a `tuple` comprehension.* **将最终生成器，而不是`tuple`理解。** *Why is that?* **这是为什么？**

*My guess is that a `tuple` is immutable, but this does not seem to be the answer.* **我的猜测是`tuple`是不可变的，但这似乎不是答案。**

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### \#1楼 ###

参考：[https://stackoom.com/question/194Wx/为什么Python中没有元组理解][https_stackoom.com_question_194Wx_Python]

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### \#2楼 ###

我最好的猜测是，他们用完了括号，并认为这对警告添加“丑陋”语法没有足够的帮助...

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### \#3楼 ###

*You can use a generator expression:* **您可以使用生成器表达式：**

tuple(i for i in (1, 2, 3))

*but parentheses were already taken for … generator expressions.* **但是对于...生成器表达式，已经使用了括号。**

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### \#4楼 ###

*I believe it's simply for the sake of clarity, we do not want to clutter the language with too many different symbols.* **我相信这只是为了清楚起见，我们不想用太多不同的符号来使语言混乱。** *Also a `tuple` comprehension is never necessary , a list can just be used instead with negligible speed differences, unlike a dict comprehension as opposed to a list comprehension.* **同样， *不需要* `tuple`理解，也可以使用速度差可以忽略的列表来代替，而不是字典理解而不是列表理解。**

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### \#5楼 ###

*Comprehension works by looping or iterating over items and assigning them into a container, a Tuple is unable to receive assignments.* **理解通过循环或迭代项并将它们分配到容器中来工作，元组无法接收分配。**

*Once a Tuple is created, it can not be appended to, extended, or assigned to.* **创建元组后，将无法对其进行追加，扩展或分配。** *The only way to modify a Tuple is if one of its objects can itself be assigned to (is a non-tuple container).* **修改元组的唯一方法是是否可以将其对象之一本身分配给它（是非元组容器）。** *Because the Tuple is only holding a reference to that kind of object.* **因为元组仅持有对此类对象的引用。**

*Also - a tuple has its own constructor `tuple()` which you can give any iterator.* **另外-元组有自己的构造函数`tuple()` ，您可以给它提供任何迭代器。** *Which means that to create a tuple, you could do:* **这意味着要创建一个元组，您可以执行以下操作：**

tuple(i for i in (1,2,3))

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### \#6楼 ###

*Raymond Hettinger (one of the Python core developers) had this to say about tuples in a [recent tweet][] :* **Raymond Hettinger（Python核心开发人员之一）在[最近的][recent tweet]一条[推文中][recent tweet]曾这样说过元组：**

> *\#python tip: Generally, lists are for looping;* **\#python提示：通常，列表用于循环；** *tuples for structs.* **结构的元组。** *Lists are homogeneous;* **列表是同质的；** *tuples heterogeneous.* **元组异构。** *Lists for variable length.* **列出可变长度。**

*This (to me) supports the idea that if the items in a sequence are related enough to be generated by a, well, generator, then it should be a list.* **（对我来说）支持这样的想法：如果序列中的项目相关性足以由生成器生成，那么它应该是一个列表。** *Although a tuple is iterable and seems like simply a immutable list, it's really the Python equivalent of a C struct:* **尽管元组是可迭代的，并且看起来只是一个不可变的列表，但它实际上与C结构的Python等效：**

struct {
        int a;
        char b;
        float c;
    } foo;
    
    struct foo x = { 3, 'g', 5.9 };

*becomes in Python* **成为Python**

x = (3, 'g', 5.9)

[Why is there no tuple comprehension in Python]: https://oldbug.net/q/194Wx/Why-is-there-no-tuple-comprehension-in-Python
[https_stackoom.com_question_194Wx_Python]: https://stackoom.com/question/194Wx/%E4%B8%BA%E4%BB%80%E4%B9%88Python%E4%B8%AD%E6%B2%A1%E6%9C%89%E5%85%83%E7%BB%84%E7%90%86%E8%A7%A3
[recent tweet]: https://twitter.com/raymondh/status/324664257004322817