09.输入一个字母判断是星期几，如果第一个字母相同就判断第二个字(dict.get()的用法)

week_day = {"m":"星期一","tu":"星期二","w":"星期三",
            "th":"星期四","f":"星期五","sa":"星期六","su":"星期日"}
fir_let = input("Please input the first letter: ")
if week_day.get(fir_let):
    print('通过%s判断是%s'%(fir_let,week_day.get(fir_let)))
else:
    if fir_let not in ['t','s']:
        print('通过输入的第一个字母未查找到对应的星期号')
    else:
        sec_let =input("Please input the second letter: ")
        if week_day.get(fir_let+sec_let):
            print('通过%s判断是%s'%(fir_let+sec_let,week_day.get(fir_let+sec_let)))
        else:
            print('通过输入的2个字母未查找到')