求帮我修改一下爬虫，能把它改成多线程的吗？初学 py！求帮帮忙，找的别人的源码！

# -*- coding: utf-8 -*-
import urllib2
import sys
#BeautifulSoup3不需要修改，BeautifulSoup4，改成from bs4 import BeautifulSoup
from BeautifulSoup import BeautifulSoup

reload(sys)
sys.setdefaultencoding( "utf-8" )

def getcontent(url):
print url
req = urllib2.Request(url)
res = urllib2.urlopen(req)
magnetlist=[]
html = res.read()
res.close()
soup = BeautifulSoup(html)
#BeautifulSoup3不需要修改，BeautifulSoup4，改成soup.find_all('a')
allentry=soup.findAll('a')
for link in allentry:
if "magnet:"==link.get('href')[0:7]:
magnetlist.append(link.get('href'))
magnetlist = [line+'\n' for line in magnetlist]
f =open("magnet.txt", "a")
f.writelines(magnetlist)
f.close()

def main():
site="http://bt.shousibaocai.com/search/"
keyword="地心引力"
keyword=urllib2.quote(keyword)
#总共抓前多少页
page=3
for i in range(1,page):
searchurl=site+keyword+"/"+str(i)
getcontent(searchurl)

if __name__ == '__main__':
main()
#end Jarett