在 Python 中使用花括号初始化 Set
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Use curly braces to initialize a Set in Python
提问by fvrghl
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合的新手问题。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:
与以下标准方式相比，这样做是否有任何缺点：
my_set = set(['foo', 'bar', 'baz'])
or is it just a question of style?
还是只是风格问题？
采纳答案by bgporter
There are two obvious issues with the set literal syntax:
集合文字语法有两个明显的问题：
my_set = {'foo', 'bar', 'baz'}
It's not available before Python 2.7
There's no way to express an empty set using that syntax (using
{}creates an empty dict)
它在 Python 2.7 之前不可用
无法使用该语法表达空集（使用
{}创建空字典）
Those may or may not be important to you.
这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.
概述此语法的文档部分是here。
回答by 0x90
From Python 3 documentation(the same holds for python 2.7):
从Python 3 文档（同样适用于 python 2.7）：
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，我们将在下一节讨论这种数据结构。
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，{}它也用于map/ dict：
>>> m = {'a':2,3:'d'}
>>> m[3]
'd'
>>> m={}
>>> type(m)
<type 'dict'>
One can also use comprehensive syntax to initialize sets:
还可以使用综合语法来初始化集合：
>>> 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', '{', '}'])
回答by Thruston
Compare also the difference between {}and set()with a single word argument.
还比较{}和set()与单个单词参数之间的差异。
>>> a = set('aardvark')
>>> a
{'d', 'v', 'a', 'r', 'k'}
>>> b = {'aardvark'}
>>> b
{'aardvark'}
but both aand bare sets of course.
但两者a和b当然都是套。
回答by Arjjun
You need to do empty_set = set()to initialize an empty set. {}is am empty dictionaty.
您需要 empty_set = set()初始化一个空集。{}是空话。
