想问一下代码哪出问题了

grades = {'A': (90,100), 'B': (80,90),
'C': (70,80), 'D': (60,70),
'F':(0,60)}

def main(score):
if score<0 or score>100:
return '无效成绩。'
else:
for grade, value in grades.item():
if int(score) in range(value):
return grade

按你这么放代码，我们是看不出问题的

item --> items
range(value)-->value