在Python中查找所有可能的大小写排列

def all_casings(input_string):    if not input_string:        yield ""    else:        first = input_string[:1]        if first.lower() == first.upper(): for sub_casing in all_casings(input_string[1:]):     yield first + sub_casing        else: for sub_casing in all_casings(input_string[1:]):     yield first.lower() + sub_casing     yield first.upper() + sub_casing

>>> [x for x in all_casings("foo")]['foo', 'Foo', 'fOo', 'FOo', 'foO', 'FoO', 'fOO', 'FOO']>>> list(all_casings("foo"))['foo', 'Foo', 'fOo', 'FOo', 'foO', 'FoO', 'fOO', 'FOO']