python实现复制指定数量文件到指定目录，出现了一点小问题

import os
import shutil
import random

filenum=100
root="C:/Users/lym/Desktop/20_newsgroups/alt.atheism"
newname="C:/Users/lym/Desktop/train"
name_lst =list(os.path.join(root, name) for name in os.listdir(root))
random_name_lst = list(random.choice(name_lst) for _ in range(0,filenum))
i=0
for _ in random_name_lst:
oldname= random_name_lst[i]
i=i+1
shutil.copy(oldname,newname)