Python基础问题Sn=1-3+5-7+9...请问大家我怎么改是对的

请问这个该怎么写，我怎么改，或者有没有更好的方法，谢谢大家的帮助。

Sn = 0
an = 0
bn = 0
n = int(input('请输入n：'))
for a in range(1, n+1):
    if a % 2 != 0:
        an = 2 * a - 1
        bn = 0
    else:
        bn = 2 * a - 1
        an = 0
    Sn += (-1) ** (a-1) * (an + bn)
print("Sn = ", Sn)

也可以这样写：

n = int(input())
print(sum((-1)**i*(2*i+1) for i in range(n)))

而如果你观察结果，就会发现等价于这个计算公式的O(1)算法的规律：

n = int(input())
if n & 1:
    print(n)
else:
    print(-n)

• 这篇博客: python根据服务器sn号查询DELL服务器型号、出厂时间、过保时间中的 多线程版本 部分也许能够解决你的问题, 你可以仔细阅读以下内容或跳转源博客中阅读:
  

• import requests,re,time
  from requests.exceptions import RequestException
  from concurrent.futures import ThreadPoolExecutor
  import threading
  base_url='https://www.dell.com/support/home/cn/zh/cnbsd1/product-support/servicetag/'
  def Get_Page(url):      #根据sn号获取返回页面
      try:
          response = requests.get(url)
          if response.status_code == 200:
              return response.text
          return None
      except RequestException:
          return None
  
  def Get_Info(s_code,sn):       #根据返回码，获取信息
      url_params = {"serviceTag":s_code}
      info_url='https://www.dell.com/support/components/dashboard/cn/zh/cnbsd1/Warranty/GetWarrantyDetails'
      r1=requests.post(info_url,data=url_params)
      h1=r1.text
      p_date=re.compile("<td>(\d+) (\d+)&#x6708; (\d+)</td>")
      p_in_date=re.compile('<td><b>(.*)(\d{2}) (\d+)&#x6708; (\d+)</b></td>')
      date2='error'
      if h1:
          c=h1.split("\n")
          for i in c:
              if '<td>NBD' in i:              #检测下一个工作日服务（优先级以上门服务器日期为准）
                  n=c.index(i)
                  # date1=p_date.findall(c[n+1])
                  date2=p_date.findall(c[n+2])
              elif '%s</b></td>'%sn in i:
                  n = c.index(i)
                  date1=p_in_date.findall(c[n+1])
                  # print(date1)
          if date2=='error':				#因为服务器型号不用，包含的服务不同，所以下面做了较多的判断
              for i in c:
                  if '<td>POW' in i:          #检查部件保修服务
                      n = c.index(i)
                      date2 = p_date.findall(c[n + 2])
                  elif '<td>4' in i:      #检查24小时上门
                      n = c.index(i)
                      date2 = p_date.findall(c[n + 2])
                  if date2=='error':
                      date2=[('error','error','error')]   #返回错误数据
                  in_date = ((date1[0][3] + '-' + date1[0][2] + '-' + date1[0][1]))  # 格式化日期
                  out_date = ((date2[0][2] + '-' + date2[0][1] + '-' + date2[0][0]))
          else:
              in_date = ((date1[0][3] + '-' + date1[0][2] + '-' + date1[0][1]))  # 格式化日期
              out_date = ((date2[0][2] + '-' + date2[0][1] + '-' + date2[0][0]))
  
          return in_date,out_date
  def write_data(server_mode,date,sn):
      server_mode = server_mode
      server_in_date = date[0]
      server_out_date = date[1]
      info_detail = sn + '\t' + server_mode + '\t' + server_in_date + '\t' + server_out_date + '\n'
      print(server_mode)
      print(server_in_date)
      print(server_out_date)
      with open('D:snlist.txt', 'a', encoding='utf-8') as ff:
          ff.write(info_detail)
  
  class DELLINFO():
      def __init__(self,sn):
          self.sn=sn
  
      def Get_Dellinfo(sn):  # 主程序
          html1 = Get_Page(base_url + sn)
          if html1:
              p1 = re.compile('servicetag/(.*)/overview"')
              p2 = re.compile('<h1 class="mb-3 mb-lg-1 text-center text-lg-left position-relative word-break">(.*)</h1>')
              r1 = p1.findall(html1)  # 过滤获取返回码
              r2 = p2.findall(html1)
              if r1 and len(r1) == 1:
                  date = Get_Info(r1[0],sn)
              if r2 and len(r2) == 1:
                  server_mode = r2[0]
          write_data(server_mode,date,sn)
  
  if __name__=='__main__':
      t_list = []
      sn_list=[]
      pool=ThreadPoolExecutor(10)
      # freeze_support()
      with open('D:\sn.txt','r',encoding='utf-8') as f:
          for i in f.readlines():
              sn_list.append(i.strip())
              t = threading.Thread(target=DELLINFO.Get_Dellinfo, args=(i.strip(),))
              t_list.append(t)
              t.start()
          for t in t_list:
              t.join()