Python 集差与集减的区别
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Difference between set difference and set subtraction
提问by David542
Is there any difference between the following two statements?
以下两种说法有区别吗？
s1 = set([1,2,3])
s2 = set([3,4,5])
>>> s1 - s2
set([1, 2])
>>> s1.difference(s2)
set([1, 2])
采纳答案by Padraic Cunningham
set.difference, set.union...can take any iterableas the second arg while both need to be sets to use -, there is no difference in the output.
set.difference, set.union...可以将任何可迭代对象作为第二个参数，而两者都需要设置为 use -，输出没有区别。
Operation Equivalent Result
s.difference(t) s - t new set with elements in s but not in t
With .difference you can do things like:
使用 .difference 您可以执行以下操作：
s1 = set([1,2,3])
print(s1.difference(*[[3],[4],[5]]))
{1, 2}
It is also more efficient when creating sets using the *(iterable,iterable)syntax as you don't create intermediary sets, you can see some comparisons here
使用*(iterable,iterable)语法创建集合时也更有效，因为您不创建中间集合，您可以在此处查看一些比较
回答by Brad Richardson
The documentation appears to suggest that difference can take multiple sets, so it is possible that it might be more efficient and clearer for things like:
该文档似乎表明差异可能需要多组，因此对于以下内容可能更有效和更清晰：
s1 = set([1, 2, 3, 4])
s2 = set([2, 5])
s3 = set([3, 6])
s1.difference(s2, s3) # instead of s1 - s2 - s3
but I would suggest some testing to verify.
但我建议进行一些测试来验证。
回答by Abhijit
On a quick glance it may not be quite evident from the documentationbut buried deep inside a paragraph is dedicated to differentiate the method call with the operator version
快速浏览一下，文档中可能不太明显，但埋藏在一个段落深处，专门用于区分方法调用与操作符版本
Note, the non-operator versions of union(), intersection(), difference(), and symmetric_difference(), issubset(), and issuperset() methods will accept any iterable as an argument. In contrast, their operator based counterparts require their arguments to be sets. This precludes error-prone constructions like
set('abc') & 'cbs'in favor of the more readableset('abc').intersection('cbs').
请注意，union()、intersection()、difference() 和 symmetric_difference()、issubset() 和 issuperset() 方法的非运算符版本将接受任何可迭代对象作为参数。相比之下，它们的基于运算符的对应物需要设置它们的参数。这排除了容易出错的结构，例如
set('abc') & 'cbs'支持更具可读性的set('abc').intersection('cbs').
