Python：这里使用[]是什么意思？

发布于 2024-09-24 13:10:53 字数 413 浏览 5 评论 0原文

python中这两个语句有什么区别？

var = foo.bar

我

var = [foo.bar]

认为它正在将 var 放入包含 foo.bar 的列表中，但我不确定。另外，如果这是行为并且 foo.bar 已经是一个列表，那么在每种情况下你会得到什么？

例如：如果 foo.bar = [1, 2] 我会得到这个吗？

var = foo.bar #[1, 2]

和

var = [foo.bar] #[[1,2]] where [1,2] is the first element in a multidimensional list

原文

What is the difference in these two statements in python?

var = foo.bar

and

var = [foo.bar]

I think it is making var into a list containing foo.bar but I am unsure. Also if this is the behavior and foo.bar is already a list what do you get in each case?

For example: if foo.bar = [1, 2] would I get this?

var = foo.bar #[1, 2]

and

var = [foo.bar] #[[1,2]] where [1,2] is the first element in a multidimensional list

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拧巴小姐 2024-10-01 13:10:54

[] 是一个空列表。

[foo.bar] 正在创建一个新列表 ([])，其中 foo.bar 作为列表中的第一项，然后可以由其索引引用：

var = [foo.bar]
var[0] == foo.bar # returns True

所以您猜测您对 foo.bar = [1,2] 的分配是完全正确的。

如果您还没有这样做，我建议您在 Python 交互式解释器中尝试一下这种事情。这使得事情变得非常简单：

>>> []
[]
>>> foobar = [1,2]
>>> foobar
[1, 2]
>>> [foobar]
[[1, 2]]

[] is an empty list.

[foo.bar] is creating a new list ([]) with foo.bar as the first item in the list, which can then be referenced by its index:

var = [foo.bar]
var[0] == foo.bar # returns True

So your guess that your assignment of foo.bar = [1,2] is exactly right.

If you haven't already, I recommend playing around with this kind of thing in the Python interactive interpreter. It makes it pretty easy:

>>> []
[]
>>> foobar = [1,2]
>>> foobar
[1, 2]
>>> [foobar]
[[1, 2]]

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阳光①夏 2024-10-01 13:10:54

是的，它正在创建一个包含一个元素 foo.bar 的列表。

如果 foo.bar 是 [1,2]，您确实会得到 [[1,2]]。

例如，

>> a=[]
>> a.append([1,2])
>> a[0] 
[1,2]
>> b=[[1,2]]
>> b[0]
[1,2]

为了详细说明这个确切的例子，

>> class Foos:
>>   bar=[1,2]
>> foo=Foos()
>> foo.bar
[1,2]
>> a=[foo.bar]
>> a
[[1,2]]
>> a[0]
[1,2]

Yes, it's making a list containing one element, foo.bar.

If foo.bar is [1,2], you indeed get [[1,2]].

For instance,

>> a=[]
>> a.append([1,2])
>> a[0] 
[1,2]
>> b=[[1,2]]
>> b[0]
[1,2]

To elaborate a bit more on that exact example,

>> class Foos:
>>   bar=[1,2]
>> foo=Foos()
>> foo.bar
[1,2]
>> a=[foo.bar]
>> a
[[1,2]]
>> a[0]
[1,2]

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御弟哥哥 2024-10-01 13:10:54

我认为它正在将 var 放入包含 foo.bar 的列表中，但我不确定。另外，如果这是行为并且 foo.bar 已经是一个列表，那么在每种情况下您会得到什么？

是的，它创建了一个新列表。
如果foo.bar已经是一个列表，它将简单地变成一个列表，包含一个列表。
<前><代码>h[1]>>>> l = [1, 2]
h[1]>>>> [l]
[[1, 2]]
h[3]>>>>升[升][0]
[1, 2]

I think it is making var into a list containing foo.bar but I am unsure. Also if this is the behavior and foo.bar is already a list what do you get in each case?

Yes, it creates a new list.
If foo.bar is already a list, it will simply become a list, containing one list.
```
h[1] >>> l = [1, 2]
h[1] >>> [l]
[[1, 2]]
h[3] >>> l[l][0]
[1, 2]
```

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