如何获得Case Insensitive Python SET

Question

我有一个字符串列表:

In [53]: l = ['#Trending', '#Trending', '#TrendinG', '#Yax', '#YAX', '#Yax']

In [54]: set(l)
Out[54]: {'#TrendinG', '#Trending', '#YAX', '#Yax'}

我想对此列表不区分大小写 set.

预期结果:

Out[55]: {'#Trending', '#Yax'}

我怎样才能做到这一点？

Answer 1

如果您需要保留大小写,则可以使用字典.小写键,然后提取值:

 set({v.casefold(): v for v in l}.values())

您可以将其封装到一个类中.

如果您不关心保留大小写,只需使用一组:

>>> print(s := 'Wa??er?chloß', s.lower(), s.casefold(), sep=" - ")
Wa??er?chloß - wa??er?chloß - wasserschloss

演示:

{v.casefold() for v in l}

将第一种方法包装到类中看起来像:

>>> l = ['#Trending', '#Trending', '#TrendinG', '#Yax', '#YAX', '#Yax']
>>> set({v.casefold(): v for v in l}.values())
{'#Yax', '#TrendinG'}
>>> {v.lower() for v in l}
{'#trending', '#yax'}

用法演示:

try:
    # Python 3
    from collections.abc import MutableSet
except ImportError:
    # Python 2
    from collections import MutableSet

class CasePreservingSet(MutableSet):
    def __init__(self, *values):
        self._values = {}
        try:
            self._fold = str.casefold  # Python 3
        except AttributeError:
            self._fold = str.lower     # Python 2
        for v in values:
            self.add(v)

    def __repr__(self):
        return '<{}{} at {:x}>'.format(
            type(self).__name__, tuple(self._values.values()), id(self))

    def __contains__(self, value):
        return self._fold(value) in self._values

    def __iter__(self):
        try:
            # Python 2
            return self._values.itervalues()
        except AttributeError:
            # Python 3
            return iter(self._values.values())

    def __len__(self):
        return len(self._values)

    def add(self, value):
        self._values[self._fold(value)] = value

    def discard(self, value):
        try:
            del self._values[self._fold(value)]
        except KeyError:
            pass