python 多线程将大文件分开下载后在合并的实例

import threading
import requests
import time
import os


class Mythread(threading.Thread):
  def __init__(self,url,startpos,endpos,f):
    super(Mythread,self).__init__()
    self.url=url
    self.startpos=startpos
    self.endpos=endpos
    self.fd=f
  def download(self):
    print(\'start thread:%s at %s\'%(self.getName(),time.time()))
    headers={\'Range\':\'bytes=%s-%s\'%(self.startpos,self.endpos)}
    res=requests.get(self.url,headers=headers)
    self.fd.seek(self.startpos)
    self.fd.write(res.content)
    print(\'Stop thread:%s at%s\'%(self.getName(),time.time()))
    self.fd.close()
  def run(self):
    self.download()
if __name__==\"__main__\":
  url=\'http://www.wendangxiazai.com/word/b-cfbdc77931b765ce050814a9-1.doc\'
  filename=url.split(\'/\')[-1]
  filesize=int(requests.head(url).headers[\'Content-Length\'])
  print(\'%s filesize:%s\'%(filename,filesize))


  threadnum=3
  threading.BoundedSemaphore(threadnum)#允许线程个数
  step=filesize//threadnum
  mtd_list=[]
  start=0
  end=-1
  
  tempf = open(\'E:\\Python\\py\\web\'+filename,\'w\')
  tempf.close()
  mtd_list=[]
  with open(\'E:\\Python\\py\\web\'+filename,\'rb+\')as f:
    #获得文件句柄
    fileno=f.fileno()#返回一个整型的文件描述符，可用于底层操作系统的 I/O 操作
    while end<filesize-1:
      start=end+1
      end=start+step-1
      if end>filesize:
        end=filesize
      print (\'Start:%s,end:%s\'%(start,end))
      dup=os.dup(fileno)#复制文件句柄
      fd=os.fdopen(dup,\'rb+\',-1)
      t=Mythread(url,start,end,fd)
      t.start()
      mtd_list.append(t)
    for i in mtd_list:
      i.join()
  f.close()