python 多线程下载图片

接上一篇，因为图片量太大，所以试着用多线程来下载图片不知道会不会快一点，我将每个收藏夹内的所有图片的url放在url_list的列表中，然后将列表中的url分成100份，分配给100个线程同时下载，用切片来分割列表
尝试多线程的时候，发现线程数量不能过多，线程数量过多，程序会报内存错误

兴趣是第一生产力

#-*-coding:utf-8-*-
import sys
import os
import Spider
import requests
import threading
import time
reload(sys)
sys.setdefaultencoding('utf-8')

def downloadImg(url_list,path,start,end):
    print('thread %s is running...' % threading.current_thread().name)
    ss = requests.session()
    thread_name = threading.current_thread().name
    img_count = 0
    for img_url in url_list[start:end]:
        #time.sleep(1)
        print "%s正在下载%d/%d张图" % (thread_name,img_count,end - start)
        img_content = ss.get(img_url)
        name = img_url.split(".")
        with open(os.path.join(path,thread_name + "_"+str(img_count) +"."+name[-1]),'wb') as f:
            f.write(img_content.content)
        img_count = img_count + 1

    print('thread %s ended.' % threading.current_thread().name)



def downCollection(collection):
    l = Spider.Login()
    s = l.login_zhihu("[email protected]","xxxxxxxx")
    parser = Spider.parserHtml()
    collection = collection.encode('utf-8')
    collection = collection.strip('\n')
    div_list = parser.getAnswerDiv_collection(collection,s)
    print "div_list length %d" % len(div_list)
    url_list = parser.getImgURL_collection(div_list)
    print "url_list length %d" % len(url_list)
    path = os.path.join(os.path.abspath("."),"sou"+collection)
    if not os.path.isdir(path):
        os.mkdir(path)
    download = Spider.Download()
    #download.downloadImg(url_list,path)
    thread_count = 1
    thread = []
    interval = len(url_list) / 100
    start = 0
    end = interval
    while end < len(url_list):
        t = threading.Thread(target=downloadImg,args=(url_list,path,start,end),name="Thread" + str(thread_count))
        thread.append(t)
        start = end
        end = end + interval
        thread_count = thread_count + 1
    for t in thread:
        t.start()
    for t in thread:
        t.join()

if __name__ == '__main__':
    downCollection("12345678")