在Python中，方括号和圆括号括起来的列表之间有什么区别?

>>> x=[1,2]
>>> x[1]
2
>>> x=(1,2)
>>> x[1]
2

Are they both valid? Is one preferred for some reason?

他们都是有效的吗?出于某种原因，你更喜欢它吗?

6 个解决方案

#1

194

Square brackets are lists while parentheses are tuples.

方括号是列表，圆括号是元组。

A list is mutable, meaning you can change its contents:

列表是可变的，这意味着您可以更改它的内容:

>>> x = [1,2]
>>> x.append(3)
>>> x
[1, 2, 3]

while tuples are not:

虽然元组不:

>>> x = (1,2)
>>> x
(1, 2)
>>> x.append(3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'tuple' object has no attribute 'append'

The other main difference is that a tuple is hashable, meaning that you can use it as a key to a dictionary, among other things. For example:

另一个主要区别是，tuple是可洗的，这意味着您可以将它用作字典的键，以及其他的东西。例如:

>>> x = (1,2)
>>> y = [1,2]
>>> z = {}
>>> z[x] = 3
>>> z
{(1, 2): 3}
>>> z[y] = 4
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'

Note that, as many people have pointed out, you can add tuples together. For example:

注意，正如许多人指出的，您可以将元组添加到一起。例如:

>>> x = (1,2)
>>> x += (3,)
>>> x
(1, 2, 3)

However, this does not mean tuples are mutable. In the example above, a new tuple is constructed by adding together the two tuples as arguments. The original tuple is not modified. To demonstrate this, consider the following:

然而，这并不意味着元组是可变的。在上面的示例中，通过将两个元组相加作为参数来构造一个新的元组。原始元组没有被修改。要证明这一点，请考虑以下几点:

>>> x = (1,2)
>>> y = x
>>> x += (3,)
>>> x
(1, 2, 3)
>>> y
(1, 2)

Whereas, if you were to construct this same example with a list, y would also be updated:

然而，如果你用列表构造同样的例子，y也会被更新:

>>> x = [1, 2]
>>> y = x
>>> x += [3]
>>> x
[1, 2, 3]
>>> y
[1, 2, 3]

#2

They are not lists, they are a list and a tuple. You can read about tuples in the Python tutorial. While you can mutate lists, this is not possible with tuples.

它们不是列表，它们是列表和元组。您可以在Python教程中阅读有关元组的内容。虽然您可以更改列表，但元组是不可能的。

In [1]: x = (1, 2)

In [2]: x[0] = 3
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)

/home/user/<ipython console> in <module>()

TypeError: 'tuple' object does not support item assignment

#3

The first is a list, the second is a tuple. Lists are mutable, tuples are not.

第一个是列表，第二个是元组。列表是可变的，元组不是。

Take a look at the Data Structures section of the tutorial, and the Sequence Types section of the documentation.

请看本教程的数据结构部分和文档的序列类型部分。

#4

Comma-separated items enclosed by ( and ) are tuples, those enclosed by [ and ] are lists.

由(和)包围的逗号分隔的项目是元组，由[和]包围的项目是列表。

#5

Another way brackets and parentheses differ is that square brackets can describe a list comprehension, e.g. [x for x in y]

方括号和括号的另一个不同之处是方括号可以描述列表理解，例如[x代表y中的x]

Whereas the corresponding parenthetic syntax specifies a tuple generator: (x for x in y)

而相应的括号语法指定了一个元组生成器:(x代表y中的x)

You can get a tuple comprehension using: tuple(x for x in y)

您可以使用:tuple(x代表y中的x)获得元组理解

See: Why is there no tuple comprehension in Python?

看:为什么Python中没有元组理解?

#6

One interesting difference that's worth noticing is when only a single value is there.

值得注意的一个有趣的差异是当只有一个值时。

lst=[1]
print lst          // prints [1]
print type(lst)    // prints <type 'list'>

notATuple=(1)
print notATuple        // prints 1
print type(notATuple)  // prints <type 'int'>
                                         ^^ instead of tuple(expected)

A comma must be included in a tuple even if it contains only a single value. e.g. (1,) instead of (1).

一个逗号必须包含在一个元组中，即使它只包含一个值。例:1，而不是1。

#1

194