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://jb51.net/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 sys

import os

import time

import urllib

from threading import Thread

# in case you want to use http_proxy

local_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={})