请教一下红字那一行: x = raw_input("input a binary number : ") result = 0 y = 1 for i in range(len(x)-1,-1,-1): d = int(x[i]) result = result + d*y y = y*2 print("the decimal equivalent of %s os %s" %(x,result)) 请问,(len(x)-1,-1,-1) 里面这三项,每项代表什么意思? 麻烦高手解答了...... ps:我只懂 range(1,x+1) 是指 1~x......