Python中的集合不区分大小写的比较 [英] Case-insensitive comparison of sets in Python

问题描述

我有两套（虽然我可以做列表，或其他）：

I have two sets (although I can do lists, or whatever):

a = frozenset(('Today','I','am','fine'))
b = frozenset(('hello','how','are','you','today'))

我想得到：

frozenset(['Today'])

或至少：

frozenset(['today'])

第二个选项是可行的，如果我低估我推测的一切，但我正在寻找一个更优雅的方式。是否可以执行

The second option is doable if I lowercase everything I presume, but I'm looking for a more elegant way. Is it possible to do

a.intersection(b) 

以不区分大小写的方式？

in a case-insensitive manner?

Django中的快捷键也很好，因为我正在使用该框架。

Shortcuts in Django are also fine since I'm using that framework.

下面的交点方法示例（我无法弄清楚如何在评论中获得此格式）：

Example from intersection method below (I couldn't figure out how to get this formatted in a comment):

print intersection('Today I am fine tomorrow'.split(),
                    'Hello How a re you TODAY and today and Today and Tomorrow'.split(),
                    key=str.lower)

[(['tomorrow'], ['Tomorrow']), (['Today'], ['TODAY', 'today', 'Today'])]

推荐答案

这是适用于任何对的版本的迭代：

Here's version that works for any pair of iterables:

def intersection(iterableA, iterableB, key=lambda x: x):
    """Return the intersection of two iterables with respect to `key` function.

    """
    def unify(iterable):
        d = {}
        for item in iterable:
            d.setdefault(key(item), []).append(item)
        return d

    A, B = unify(iterableA), unify(iterableB)

    return [(A[k], B[k]) for k in A if k in B]

示例：

print intersection('Today I am fine'.split(),
                   'Hello How a re you TODAY'.split(),
                   key=str.lower)
# -> [(['Today'], ['TODAY'])]

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