Python 创建一个空集
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Creating an empty set
提问by Chris Degnen
I have some code which tots up a set of selected values. I would like to define an empty set and add to it, but {}keeps turning into a dictionary. I have found if I populate the set with a dummy value I can use it, but it's not very elegant. Can someone tell me the proper way to do this? Thanks.
我有一些代码可以汇总一组选定的值。我想定义一个空集并添加到它，但{}一直变成字典。我发现如果我用一个虚拟值填充集合，我可以使用它，但它不是很优雅。有人可以告诉我这样做的正确方法吗？谢谢。
inversIndex = {'five': {1}, 'ten': {2}, 'twenty': {3},
'two': {0, 1, 2}, 'eight': {2}, 'four': {1},
'six': {1}, 'seven': {1}, 'three': {0, 2},
'nine': {2}, 'twelve': {2}, 'zero': {0, 1, 3},
'eleven': {2}, 'one': {0}}
query = ['four', 'two', 'three']
def orSearch(inverseIndex, query):
b = [ inverseIndex[c] for c in query ]
x = {'dummy'}
for y in b:
{ x.add(z) for z in y }
x.remove('dummy')
return x
orSearch(inverseIndex, query)
{0, 1, 2}
{0, 1, 2}
采纳答案by Jon Kiparsky
You can just construct a set:
你可以构造一个集合：
>>> s = set()
will do the job.
会做的工作。
回答by inspectorG4dget
The "proper" way to do it:
“正确”的方式来做到这一点：
myset = set()
The {...}notation cannot be used to initialize an empty set
该{...}符号不能用于初始化空集
回答by Jon Clements
As has been pointed out - the way to get an empy setliteral is via set(), however, if you re-wrote your code, you don't need to worry about this, eg (and using set()):
正如已经指出的那样 - 获得 empyset文字的方法是 via set()，但是，如果您重新编写代码，则无需担心这一点，例如（并使用set()）：
from operator import itemgetter
query = ['four', 'two', 'three']
result = set().union(*itemgetter(*query)(inversIndex))
# set([0, 1, 2])
回答by pycoder
A set literal is just a tupleof values in curly braces:
集合文字只是花括号中的一组值：
x = {2, 3, 5, 7}
So, you can create an empty set with empty tupleof values in curly braces:
因此，您可以使用花括号中的空值元组创建一个空集：
x = {*()}
Still, just because you can, doesn't mean you should.
尽管如此，仅仅因为你可以，并不意味着你应该。
Unless it's an obfuscated programming, or a codegolfwhere every character matters, I'd suggest an explicit x = set()instead.
除非它是一个混淆的编程，或者每个字符都很重要的codegolf，否则我建议使用显式x = set()。
