如果需要保留大小写，可以改用字典。大小写折叠键，然后将值提取到集合中：
set({v.casefold(): v for v in l}.values())
该str.casefold()方法使用Unicode大小写折叠规则（pdf）来规范化字符串，以进行不区分大小写的比较。这对于非ASCII字母和带连字的文本尤其重要。例如，德国ß尖锐的S，将其标准化为longss，或者从相同的语言标准化为slong：
>>> print(s := 'Wa??er?chloß', s.lower(), s.casefold(), sep=" - ")
Wa??er?chloß - wa??er?chloß - wasserschloss
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set理解即可：
{v.casefold() for v in l}
注意，Python 2没有这种方法，请str.lower()在这种情况下使用。
演示：
>>> 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'}
将第一种方法包装到类中将如下所示：
try:
# Python 3
from collections.abc import MutableSet
except ImportError:
# Python 2
from collections import MutableSet
class CasePreservingSet(MutableSet):
"""String set that preserves case but tests for containment by case-folded value
E.g. 'Foo' in CasePreservingSet(['FOO']) is True. Preserves case of *last*
inserted variant.
"""
def __init__(self, *args):
self._values = {}
if len(args) > 1:
raise TypeError(
f"{type(self).__name__} expected at most 1 argument, "
f"got {len(args)}"
)
values = args[0] if args else ()
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
用法演示：
>>> cps = CasePreservingSet(l)
>>> cps
<CasePreservingSet('#TrendinG', '#Yax') at 1047ba290>
>>> '#treNdinG' in cps
True
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