python爬虫中，出现ValueError: can only parse strings该如何解决？

[Alex-7c]

如题，本人用Python爬取内容时，出现了ValueError: can only parse strings这个错误，该如何解决？

源代码如下：
#-*-coding:utf8-*-

from lxml import etree
from multiprocessing.dummy import Pool as ThreadPool
import requests
import json
import sys

reload(sys)

sys.setdefaultencoding('utf-8')

def towrite(contentdict):
f.writelines(u'回帖时间：' + str(contentdict['topic_reply_time'])+'\n')
f.writelines(u'回帖内容：' + unicode(contentdict['topic_reply_content'])+'\n')
f.writelines(u'回帖人：' + contentdict['user_name']+'\n\n')

def spider(url):
html=requests.get(url)
selector=etree.HTML(html)
content_field=selector.xpath('//div[@class="l_post j_l_post l_post_bright "]')
item={}
for each in content_field:
reply_info=json.load(each.xpath('@data-field')[0].replace('"',''))
author=reply_info['author']['user_name']
content=each.xpath('div[@class="d_post_content_main"]/div/cc/div[@class="d_post_content j_d_post_content clearfix"]/text()')[0]
reply_time=reply_info['content']['date']
print author
print content
print reply_time
item['user_name']=author
item['topic_reply_content']=content
item['topic_reply_time']=reply_time
towrite(item)

if __name__=='__main__':
pool=ThreadPool(4)
f=open('content.txt','a')
page=[]
for i in range(1,21):
newpage='http://tieba.baidu.com/p/3522395718?pn='+str(i)
page.append(newpage)

results=pool.map(spider, page)
pool.close()
pool.join()
f.close()

[Alex-7c]

results=pool.map(spider, page) 这一句出现错误

[Alex-7c]

引用 1 楼 u012536120 的回复:

值错误：只能解析string 你是哪句报错？肯定是你某个方法传入了非string的参数，所以报错

results=pool.map(spider, page) 这一句出现错误

[sanGuo_uu]

值错误：只能解析string 你是哪句报错？肯定是你某个方法传入了非string的参数，所以报错

[yy19931231]

我也是这个报错