AttributeError: 'module' object has no attribute 'OP_SINGLE_ECDH_USE'

When I use Scrapy to write a spider, I keep getting this error. Here is my code:

# -*- coding: utf-8 -*-
import scrapy

class ZhihuSpider(scrapy.Spider):
    name = "zhihu"
    allowed_domains = ["www.zhihu.com"]
    start_urls = ["http://www.zhihu.com"]
    def start_requests(self):
        print '\n\n\n 1 \n\n\n'
        return [scrapy.Request('http://www.zhihu.com/#signin')]
    def parse(self, response):
        print '\n\n\n2\n\n\n'
        print response