用 mongodb 编写一个简单的 python scrapy 爬虫

我已经开始编写一个简单的scrapy 模块供mongodb 使用。我是 python 新手，我写的代码有问题：

国会.py

import scrapy

from scrapy.selector import Selector
from scrapy.loader import ItemLoader
from scrapy.spiders import CrawlSpider, Rule
from scrapy.linkextractors import LinkExtractor
from scrapy.http import HtmlResponse
from congress.items import CongressItem

class CongressSpider(CrawlSpider):
    name = "congres"
    allowed_domains = ["www.congress.gov"]
    start_urls = [
            'https://www.congress.gov/members',
        ]
    #creating a rule for my crawler. I only want it to continue to the next page, don't follow any other links.
    rules = (Rule(LinkExtractor(allow=(),restrict_xpaths=("//a[@class='next']",)), callback="parse_page", follow=True),)

    def parse_page(self, response):
        for search in response.selector.xpath(".//li[@class='compact']"):
            yield {'member' : ' '.join(search.xpath("normalize-space(span/a/text())").extract()).strip(),
               'state' : ' '.join(search.xpath("normalize-space(div[@class='quick-search-member']//span[@class='result-item']/span/text())").extract()).strip(),
                'District' : ' '.join(search.xpath("normalize-space(div[@class='quick-search-member']//span[@class='result-item'][2]/span/text())").extract()).strip(),
                'party' : ' '.join(search.xpath("normalize-space(div[@class='quick-search-member']//span[@class='result-item'][3]/span/text())").extract()).strip(),
                'Served' : ' '.join(search.xpath("normalize-space(div[@class='quick-search-member']//span[@class='result-item'][4]/span//li/text())").extract()).strip(),
            }

项目.py

import scrapy
class CongressItem(scrapy.Item):
# define the fields for your item here like:
# name = scrapy.Field()

    member = scrapy.Field()
    state = scrapy.Field()
    District = scrapy.Field()
    party = scrapy.Field()
    served = scrapy.Field()

管道.py

from pymongo import MongoClient
from scrapy.conf import settings
from scrapy.exceptions import DropItem
from scrapy import log

class CongressPipeline(object):
    collection_name= 'members'
    def __init__(self, mongo_uri, mongo_db):
        self.mongo_uri = mongo_uri
        self.mongo_db = mongo_db
    @classmethod
    def from_crawler(cls, crawler):
        return cls(
            mongo_uri=crawler.settings.get('MONGO_URI'),
            mongo_db=crawler.settings.get('MONGO_DATABASE', 'items')
        )
    def open_spider(self,spider):
            self.client = pymongo.MongoClient(self.mongo_uri)
            self.db = self.client[self.mongo_db]
    def close_spider(self, spider):
        self.client.close()
    def process_item(self, item, spider):
        self.db[self.collection_name].insert(dict(item))
        return item

设置.py

BOT_NAME = 'congres'

SPIDER_MODULES = ['congres.spiders']
NEWSPIDER_MODULE = 'congres.spiders'





MONGO_URI = 'mongodb://localhost:27017'
MONGO_DATABASE = 'congres'
ROBOTSTXT_OBEY = True
DOWNLOAD_DELAY = 3
ITEM_PIPELINES = {
   'congress.pipelines.CongresPipeline': 300,
}

它显示的错误是

Unhandled error in Deferred:
2017-07-09 11:15:33 [twisted] CRITICAL: Unhandled error in Deferred:

2017-07-09 11:15:34 [twisted] CRITICAL:
Traceback (most recent call last):
File "c:\python27\lib\site-packages\twisted\internet\defer.py", line 1386, 
in _inlineCallbacks
result = g.send(result)
File "c:\python27\lib\site-packages\scrapy\crawler.py", line 95, in crawl
six.reraise(*exc_info)
File "c:\python27\lib\site-packages\scrapy\crawler.py", line 79, in crawl
yield self.engine.open_spider(self.spider, start_requests)
NameError: global name 'pymongo' is not defined