def login(username, password):
  """
  用于用戶名和密碼的驗證
  :param username:用戶名
  :param paaword:密碼
  :return:True,用戶驗證成功；False，用戶驗證失敗
  """
  try:
    f = open("users", "r", encoding="utf-8")
    for line in f:
      line = line.strip() # 清除換行符
      # 無參數(shù)時移除兩側(cè)空格，換行符
      # 有參數(shù)時移除兩側(cè)指定的字符
      line_list = line.split("$")
      if line_list[0] == username and line_list[1] == password:
        # print("成功")
        return True
    return False
  except IOError:
    return False


def register(username, password):
  """
  注冊用戶
  1、打開文件
  2、用戶名$密碼
  :param username:用戶名
  :param password:密碼
  :return:True：注冊成功；
  """
  with open("users", "a", encoding="utf-8") as f:
    temp = "\n" + username + "$" + password
    f.write(temp)
    return True


def user_exist(username):
  """
  檢測用戶名是否存在
  :param username:要檢測的用戶名
  :return: True：用戶名存在；False：用戶名不存在
  """
  # 一行一行的去查找，如果用戶名存在，return True：False
  try:
    with open("users", "r", encoding="utf-8") as f:
      for line in f:
        line = line.strip()
        line_new = line.split("$")
        if line_new[0] == username:
          return True
      return False
  except IOError:
    return False


def main():
  while True:
    print("歡迎登錄xxx系統(tǒng)")
    arg = input("1:登錄，2：注冊")

    if arg == "1":
      uer = input("請輸入用戶名:")
      pwd = input("請輸入密碼:")
      if login(uer, pwd):
        print("成功")
        break
      else:
        print("失敗")
    elif arg == "2":
      user = input("請輸入用戶名:")
      pwd = input("請輸入密碼:")
      is_exist = user_exist(user)
      if is_exist:
        print("用戶名已經(jīng)存在，注冊失敗")
      else:
        if register(user, pwd):
          print("注冊成功")
          continue
        else:
          print("注冊失敗")
    else:
      print("輸入錯誤，請重新輸入")


main()