写代码：利用下划线将列表的每个元素拼接成字符串，li=["alex","eric","rain"]

 1 #encoding: utf-8
 2 
 3 # 作业：请用代码实现：利用下划线将列表的每个元素拼接成字符串，li=["alex","eric","rain"]
 4 
 5 li = ["alex", "eric", "rain"]
 6 a = li[0]
 7 
 8 for i in li[1:]:
 9     a += "_" + i
10 
11 print(a)