python多线程http下载实现示例

花了将近两个小时， 问题主要刚开始没有想到传一个文件对象到线程里面去， 导致下载下来的文件和源文件MD5不一样，浪费不少时间.

有兴趣的同学可以拿去加上参数，改进下， 也可以加上断点续传.

代码如下:

import threading
import urllib2
import sys

max_thread = 10
# 初始化锁
lock = threading.RLock()

class Downloader(threading.Thread):
def __init__(self, url, start_size, end_size, fobj, buffer):
self.url = url
self.buffer = buffer
self.start_size = start_size
self.end_size = end_size
self.fobj = fobj
threading.Thread.__init__(self)

def run(self):
"""
马甲而已
"""
with lock:
print 'starting: %s' % self.getName()
self._download()

def _download(self):
"""
我才是搬砖的
"""
req = urllib2.Request(self.url)
# 添加HTTP Header(RANGE)设置下载数据的范围
req.headers['Range'] = 'bytes=%s-%s' % (self.start_size, self.end_size)
f = urllib2.urlopen(req)
# 初始化当前线程文件对象偏移量
offset = self.start_size
while 1:
block = f.read(self.buffer)
# 当前线程数据获取完毕后则退出
if not block:
with lock:
print '%s done.' % self.getName()
break
# 写如数据的时候当然要锁住线程
# 使用 with lock 替代传统的 lock.acquire().....lock.release()
# 需要python >= 2.5
with lock:
sys.stdout.write('%s saveing block...' % self.getName())
# 设置文件对象偏移地址
self.fobj.seek(offset)
# 写入获取到的数据
self.fobj.write(block)
offset = offset + len(block)
sys.stdout.write('done.\n')

def main(url, thread=3, save_file='', buffer=1024):
# 最大线程数量不能超过max_thread
thread = thread if thread <= max_thread else max_thread
# 获取文件的大小
req = urllib2.urlopen(url)
size = int(req.info().getheaders('Content-Length')[0])
# 初始化文件对象
fobj = open(save_file, 'wb')
# 根据线程数量计算 每个线程负责的http Range 大小
avg_size, pad_size = divmod(size, thread)
plist = []
for i in xrange(thread):
start_size = i*avg_size
end_size = start_size + avg_size - 1
if i == thread - 1:
# 最后一个线程加上pad_size
end_size = end_size + pad_size + 1
t = Downloader(url, start_size, end_size, fobj, buffer)
plist.append(t)

# 开始搬砖
for t in plist:
t.start()

# 等待所有线程结束
for t in plist:
t.join()

# 结束当然记得关闭文件对象
fobj.close()
print 'Download completed!'

if __name__ == '__main__':
url = 'http://192.168.1.2:8082/downloads/10M.zip'
main(url=url, thread=10, save_file='test.iso', buffer=4096)