python 爬取北京菜价

from concurrent.futures import ThreadPoolExecutor,ProcessPoolExecutor
import  requests
from lxml import etree
import csv

f = open('newdata5.csv', mode='w', encoding='utf-8')
csvwrite = csv.writer(f)
def one_page(url):
   response=requests.get(url)
   response.encoding='uft-8'
   demo = response.text
   html=etree.HTML(demo)
   table=html.xpath('/html/body/div[2]/div[4]/div[1]/table')[0]
   trs=table.xpath('./tr')[1:]

   for tr in trs:
    tu=tr.xpath('./td/text()')
    csvwrite.writerow(tu)
    print(tu)
   print(url,'保存完毕')


if __name__ == '__main__':
    with ThreadPoolExecutor(50) as t:#几个线程？
        for i in range(50):#爬取几个？
            t.submit(one_page,"http://www.xinfadi.com.cn/marketanalysis/0/list/{}.shtml".format(i))
    print(str(i)+"条爬取结束.........")