python长度转换

s=input()
if s[-1:] in ['m']:
    s=eval(s[0:-1])*39.37
    print("{:.3f}in".format(s))
elif s[-2:] in ['in']:
    s=eval(s[0:-2])/39.37
    print("{:.3f}m".format(s))
else:
    print("输入错误")