Scrapy爬虫管道持久化存储文件无法写入的原因是什么？

# spider.py
import scrapy
import sys
sys.path.append(r'd:\project_test\pydemo\demo1\xunlian\myspider\qiubai')
from ..items import qiubaiitem

class biedouspider(scrapy.Spider):
    name = "biedou"
    start_urls = ["https://www.biedoul.com/wenzi/"]

    def parse(self, response):
        dl_list = response.xpath('/html/body/div[4]/div[1]/div[1]/dl')

        for dl in dl_list:
            title = dl.xpath('./span/dd/a/strong/text()')[0].extract()
            content = dl.xpath('./dd//text()').extract()
            content = ''.join(content)

            item = qiubaiitem()
            item['title'] = title
            item['content'] = content
            yield item
            break

# items.py
import scrapy
class qiubaiitem(scrapy.Item):
    title = scrapy.Field()
    content = scrapy.Field()

# pipelines.py
class qiubaipipeline(object):
    def __init__(self):
        self.fp = None

    def open_spdier(self, spider):  # 拼写错误！
        print("开始爬虫")
        self.fp = open('./biedou.txt', 'w', encoding='utf-8')

    def close_spider(self, spider):
        print("结束爬虫")
        self.fp.close()

    def process_item(self, item, spider):
        title = str(item['title'])
        content = str(item['content'])
        self.fp.write(title + ':' + content + '\n')
        return item

...
typeerror: object of type qiubaiitem is not json serializable
结束爬虫
...
attributeerror: 'nonetype' object has no attribute 'close'

# pipelines.py (修正后的代码)
class QiubaiPipeline(object):
    def __init__(self):
        self.fp = None

    def open_spider(self, spider): # 修正拼写错误
        print("开始爬虫")
        self.fp = open('./biedou.txt', 'w', encoding='utf-8')

    def close_spider(self, spider):
        print("结束爬虫")
        self.fp.close()

    def process_item(self, item, spider):
        title = item['title']
        content = item['content']
        self.fp.write(f"{title}:{content}\n") # 使用f-string更简洁
        return item