input_1=raw_input('Enter the number: ')
input_1=int(input_1)
if input_1>=90 and input_1<=100:
print 'A'
if input_1>=80 and input_1<=89:
print 'B'
if input_1>=70 and input_1<=79:
print 'C'
if input_1>=60 and input_1<=69:
print 'D'
if input_1>=0 and input_1<60:
print 'F'
我也刚学,现在只能想到这么做了.继续努力.