代码如下:
def getremotefilesize(url, proxy=none):
    通过content-length头获取远程文件大小
        url - 目标文件url
        proxy - 代理 
    opener = urllib2.build_opener()
    if proxy:
        if url.lower().startswith('https://'):
            opener.add_handler(urllib2.proxyhandler({'https' : proxy}))
        else:
            opener.add_handler(urllib2.proxyhandler({'http' : proxy}))
    try:
        request = urllib2.request(url)
        request.get_method = lambda: 'head'
        response = opener.open(request)
        response.read()
    except exception, e: # 远程文件不存在       
        return 0
    else:
        filesize = dict(response.headers).get('content-length', 0)
        return int(filesize)