我们在使用for循环的时候，由于python语言的高效性，致使我们渐渐忽略了一个很重要的角色，index。
怎样查找当前记录的下一条记录呢？
li1 = [3, 4, 5, 6, 7]
i = 0
for rec in li1:
print "this record is: " + str(rec)
if i + 1 < len(li1):
print "next record is: " + str(li1[i + 1]
else:
print "the last record!"
print '\n'
i += 1
运行结果：
this record is: 3
next record is: 4
this record is: 4
next record is: 5
this record is: 5
next record is: 6
this record is: 6
next record is: 7
this record is: 7
the last record!