判断是否有ox
sample：
def xo(s):
s = str.lower(s)
s = list(s)
counto=0
countx=0
for item in s:
if item == 'o':
counto+=1
elif item =='x':
countx+=1
return counto==countx
别人的
def xo(s): s = s.lower() return s.count('x') == s.count('o')