python3 这样写为啥报错
def cmp_ignore_case(s1, s2):
if s1.upper()>s2.upper():
return-1
if s1.upper()<s2.upper():
return 1
if s1.upper()==s2.upper():
return 0
print (sorted(['bob', 'about', 'Zoo', 'Credit'],cmp_ignore_case))
