需求：
产生的账号是以@163.com结尾，长度由用户输入，产生多少条也由用户输入，用户名不能重复，用户名必须由大写字母、小写字母、数字组成
import random,string
def gen_username():
endwith = '@163.com'
success_username =0
duplicate_flag = 0 # 密码是否重复
duplicate_num = 0 # 重复的次数
with open('usernamefile.txt', 'w') as fnew: # 没有文件的话新建，已有会清空
pass
username_len = int(input('请输入用户名的长度：').strip()) #接收的为字符，需要转为int
username_num = int(input('请输入产生账号的条数：').strip())
while username_len <4:
print('用户名必须由大写、小写、数字组成，长度必须大于3，请重新输入：')
username_len = int(input('请输入用户名的长度：').strip())
else:
while success_username < username_num:
username_list = []
upper_name = random.choice(string.ascii_uppercase)
lower_name = random.choice(string.ascii_lowercase)
username_list.append(upper_name)
username_list.append(lower_name)
for digit_num in range(username_len-2):
digit_name = random.randint(0,9)
username_list.append(str(digit_name)) #要用到list 的join方法，list中的每个元素需为字符串
digit_name +=1
random.shuffle(username_list) #打乱顺序
username = ''.join(username_list) + endwith
with open('usernamefile.txt','r') as f_dup:
for line in f_dup:
if username == line:
duplicate_flag = 1
duplicate_num = duplicate_num + 1
if duplicate_flag ==0: #没有和文件里已有的用户名重复则写入
with open('usernamefile.txt','a+') as f_write:
f_write.write(username)
f_write.write('\n')
success_username += 1
else:
print("用户名生成完成，重复次数 %d" % duplicate_num)
gen_username()
