Pipelines 底下的MysqlTwistedPipeline：

class MysqlTwistedPipeline(object):
    def __init__(self, dbpool):
        self.dbpool = dbpool

    @classmethod
    def from_settings(cls, settings):
        dbparms = dict(
            host = settings["MYSQL_HOST"],
            db = settings["MYSQL_DBNAME"],
            user = settings["MYSQL_USER"],
            passwd = settings["MYSQL_PASSWORD"],
            charset = 'utf8',
            cursorclass = MySQLdb.cursors.DictCursor,
            use_unicode = True,
        )

        dbpool = adbapi.ConnectionPool("MySQLdb", **dbparms)

        return cls(dbpool)

    def process_item(self, item, spider):
        # 使用 twisted 将 mysql 插入变成异步执行
        query = self.dbpool.runInteraction(self.do_insert, item)
        query.addErrback(self.handle_error, item, spider) #处理异常

    def handle_error(self, failure, item, spider):
        # 处理异步插入的异常
        print(failure)

    def do_insert(self, cursor, item):
        # 执行具体的插入
        # 根据不同的 item 构建不同的 sql 语句并插入到 MySQL 中
        insert_sql, params = item.get_insert_sql()
        cursor.execute(insert_sql, params)

class ZhihuQuestionItem(scrapy.Item):
    #知乎的问题 item
    zhihu_id = scrapy.Field()
    topics = scrapy.Field()
    url = scrapy.Field()
    title = scrapy.Field()
    content = scrapy.Field()
    answer_num = scrapy.Field()
    comment_num = scrapy.Field()
    watch_user_num = scrapy.Field()
    click_num = scrapy.Field()
    crawl_time = scrapy.Field()

    def get_insert_sql(self):
        # 插入知乎 question 表的 SQL 语句
        insert_sql = """
            insert into zhihu_question (zhihu_id, topics, url, title, content, answer_num, 
            comments_num, watch_user_num, click_num, crawl_time)
            VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s, %s)
        """

        zhihu_id = self["zhihu_id"][0]
        topics = ",".join(self["topics"])
        url = self["url"][0]
        title = "".join(self["title"])

        content = "".join(self["content"])

        answer_num = extract_num("".join(self["answer_num"]))
        comments_num = extract_num("".join(self["comment_num"]))

        if len(self["watch_user_num"]) == 2:
            watch_user_num = self.str2int(self["watch_user_num"][0])
            click_num = self.str2int(self["watch_user_num"][1])
        else:
            watch_user_num = self.str2int(self["watch_user_num"])
            click_num = 0

        crawl_time = datetime.datetime.now().strftime(SQL_DATETIME_FORMAT)

        params = (zhihu_id, topics, url, title, content, answer_num, comments_num,
                  watch_user_num, click_num, crawl_time)

        return insert_sql, params

    def str2int(self, num):
        num = num.replace(",", "")
        return int(num)

报错内容：

[Failure instance: Traceback: <class 'KeyError'>: 'content'

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/threading.py:914:_bootstrap_inner

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/threading.py:862:run

/Users/liyang/workspaces/articlespider/lib/python3.5/site-packages/twisted/_threads/_threadworker.py:46:work

/Users/liyang/workspaces/articlespider/lib/python3.5/site-packages/twisted/_threads/_team.py:190:doWork

--- <exception caught here> ---

/Users/liyang/workspaces/articlespider/lib/python3.5/site-packages/twisted/python/threadpool.py:250:inContext

/Users/liyang/workspaces/articlespider/lib/python3.5/site-packages/twisted/python/threadpool.py:266:<lambda>

/Users/liyang/workspaces/articlespider/lib/python3.5/site-packages/twisted/python/context.py:122:callWithContext

/Users/liyang/workspaces/articlespider/lib/python3.5/site-packages/twisted/python/context.py:85:callWithContext

/Users/liyang/workspaces/articlespider/lib/python3.5/site-packages/twisted/enterprise/adbapi.py:477:_runInteraction

/Users/liyang/workspaces/articlespider/lib/python3.5/site-packages/twisted/python/compat.py:463:reraise

/Users/liyang/workspaces/articlespider/lib/python3.5/site-packages/twisted/enterprise/adbapi.py:467:_runInteraction

/Users/liyang/PythonProjects/ArticleSpider/ArticleSpider/pipelines.py:84:do_insert

/Users/liyang/PythonProjects/ArticleSpider/ArticleSpider/items.py:123:get_insert_sql

/Users/liyang/workspaces/articlespider/lib/python3.5/site-packages/scrapy/item.py:59:__getitem__

]