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Python实现多线程下载文件的代码实例
实现简单的多线程下载，需要关注如下几点：1.文件的大小：可以从reponse header中提取，如“Content-Length:911”表示大小是911字节2.任务拆分：指定各个线程下载的文件的哪一块，可以通过request header中添加“Range: bytes=300-400”（表示下载300~400byte的内容），注意可以请求的文件的range是[0, size-1]字节的。3.下载文件的聚合：各个线程将自己下载的文件块保存为临时文件，所有线程都完成后，再将这些临时文件按顺序聚合写入到最终的一个文件中。
实现代码：复制代码 代码如下:#!/usr/bin/python# -*- coding: utf-8 -*-# filename: paxel.py# FROM: http://zwyuanma.com/code/view/58/full/# Jay modified it a little and save for further potential usage.'''It is a multi-thread downloading tool It was developed following axel. Author: volans E-mail: volansw [at] gmail.com'''import sysimport osimport timeimport urllibfrom threading import Thread# in case you want to use http_proxylocal_proxies = {'http': 'http://131.139.58.200:8080'} class AxelPython(Thread, urllib.FancyURLopener): '''Multi-thread downloading class. run() is a vitural method of Thread. ''' def __init__(self, threadname, url, filename, ranges=0, proxies={}): Thread.__init__(self, name=threadname) urllib.FancyURLopener.__init__(self, proxies) self.name = threadname self.url = url self.filename = filename self.ranges = ranges self.downloaded = 0 def run(self): '''vertual function in Thread''' try: self.downloaded = os.path.getsize(self.filename) except OSError: #print 'never downloaded' self.downloaded = 0 # rebuild start poind self.startpoint = self.ranges[0] + self.downloaded # This part is completed if self.startpoint >= self.ranges[1]: print 'Part %s has been downloaded over.' % self.filename return self.oneTimeSize = 16384 # 16kByte/time print 'task %s will download from %d to %d' % (self.name, self.startpoint, self.ranges[1]) self.addheader("Range", "bytes=%d-%d" % (self.startpoint, self.ranges[1])) self.urlhandle = self.open(self.url) data = self.urlhandle.read(self.oneTimeSize) while data: filehandle = open(self.filename, 'ab+') filehandle.write(data) filehandle.close() self.downloaded += len(data) #print "%s" % (self.name) #progress = u'\r...' data = self.urlhandle.read(self.oneTimeSize) def GetUrlFileSize(url, proxies={}): urlHandler = urllib.urlopen(url, proxies=proxies) headers = urlHandler.info().headers length = 0 for header in headers: if header.find('Length') != -1: length = header.split(':')[-1].strip() length = int(length) return length def SpliteBlocks(totalsize, blocknumber): blocksize = totalsize / blocknumber ranges = [] for i in range(0, blocknumber - 1): ranges.append((i * blocksize, i * blocksize + blocksize - 1)) ranges.append((blocksize * (blocknumber - 1), totalsize - 1)) return ranges def islive(tasks): for task in tasks: if task.isAlive(): return True return False def paxel(url, output, blocks=6, proxies=local_proxies): ''' paxel ''' size = GetUrlFileSize(url, proxies) ranges = SpliteBlocks(size, blocks) threadname = ["thread_%d" % i for i in range(0, blocks)] filename = ["tmpfile_%d" % i for i in range(0, blocks)] tasks = [] for i in range(0, blocks): task = AxelPython(threadname[i], url, filename[i], ranges[i]) task.setDaemon(True) task.start() tasks.append(task) time.sleep(2) while islive(tasks): downloaded = sum([task.downloaded for task in tasks]) process = downloaded / float(size) * 100 show = u'\rFilesize:%d Downloaded:%d Completed:%.2f%%' % (size, downloaded, process) sys.stdout.write(show) sys.stdout.flush() time.sleep(0.5) filehandle = open(output, 'wb+') for i in filename: f = open(i, 'rb') filehandle.write(f.read()) f.close() try: os.remove(i) pass except: pass filehandle.close()if __name__ == '__main__': url = 'http://dldir1.qq.com/qqfile/QQforMac/QQ_V3.1.1.dmg' output = 'download.file' paxel(url, output, blocks=4, proxies={})