import threadingimport requestsimport timeimport osclass 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)#允許線程個數  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:    #獲得文件句柄    fileno=f.fileno()#返回一個整型的文件描述符，可用于底層操作系統的 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)#復制文件句柄      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()