使用Curly Braces初始化Set

I'm learning python, and I have a novice question about initializing sets. Through testing, I've discovered that a set can be initialized like so:

我正在学习python，我有一个关于初始化集的新手问题。通过测试，我发现可以像这样初始化一个集合：

my_set = {'foo', 'bar', 'baz'}

Are there any disadvantages of doing it this way, as opposed to the standard way of:

这样做是否有任何缺点，与标准方式相反：

my_set = set(['foo', 'bar', 'baz'])

or is it just a question of style?

还是只是一个风格问题？

3 个解决方案

#1

There are two obvious issues with the set literal syntax:

set字面语法有两个明显的问题：

my_set = {'foo', 'bar', 'baz'}

It's not available before Python 2.7

它在Python 2.7之前不可用
There's no way to express an empty set using that syntax (using {} creates an empty dict)

使用该语法无法表达空集（使用{}创建一个空字典）

Those may or may not be important to you.

那些对你来说可能重要，也可能不重要。

The section of the docs outlining this syntax is here.

这里概述了这种语法的文档部分。

#2

Compare also the difference between {} and set() with a single word argument.

比较{}和set（）与单个单词参数之间的区别。

>>> a = set('aardvark')
>>> a
{'d', 'v', 'a', 'r', 'k'} 
>>> b = {'aardvark'}
>>> b
{'aardvark'}

but both a and b are sets of course.

但是a和b都是套路。

#3

From Python 3 documentation (the same holds for python 2.7):

从Python 3文档（对于python 2.7同样适用）：

Curly braces or the set() function can be used to create sets. Note: to create an empty set you have to use set(), not {}; the latter creates an empty dictionary, a data structure that we discuss in the next section.

大括号或set（）函数可用于创建集合。注意：要创建一个空集，您必须使用set（），而不是{};后者创建一个空字典，一个我们将在下一节讨论的数据结构。

in python 2.7:

在python 2.7中：

>>> my_set = {'foo', 'bar', 'baz', 'baz', 'foo'}
>>> my_set
set(['bar', 'foo', 'baz'])

Be aware that {} is also used for map/dict:

请注意，{}也用于map / dict：

>>> m = {'a':2,3:'d'}
>>> m[3]
'd'
>>> m={}
>>> type(m)
<type 'dict'>

One can use sets comprehension:

可以使用集合理解：

>>> a = {x for x in """didn't know about {} and sets """ if x not in 'set' }
>>> a
set(['a', ' ', 'b', 'd', "'", 'i', 'k', 'o', 'n', 'u', 'w', '{', '}'])

#1