阿里hr面试题，scrapy实现增量式爬取，附详细答案

chapter_Content = “”.join(“”.join(text.xpath(“.//dd[@id=‘contents’]//*/text()”)))

pattern = re.compile(‘dd id=“contents”.?>(.?)’)

match = pattern.search(ht)

chapter_Content = “”.join(match.group(1).replace(" “,”").split()) if match else “爬取错误”

‘’’

result,number = re.subn(“<.*?>”,“”,str(soup.find(“dd”,id=‘contents’)))

chapter_Content = “”.join(result.split())

print(len(chapter_Content))

novel_ID = response.url.split(“/”)[-2]

return ChapterItem(

chapter_Url = response.url,

_id=int(response.url.split(“/”)[-1].split(“.”)[0]),

novel_Name=novel_Name,

chapter_Name=chapter_Name,

chapter_Content= chapter_Content,

novel_ID = novel_ID,

is_Error = len(chapter_Content) < 3000

)

3.scrapy中实现增量式爬取的几种方式

1.缓存

通过开启缓存，将每个请求缓存至本地，下次爬取时，scrapy会优先从本地缓存中获得response，这种模式下，再次请求已爬取的网页不用从网络中获得响应，所以不受带宽影响，对服务器也不会造成额外的压力，但是无法获取网页变化的内容，速度也没有第二种方式快，而且缓存的文件会占用比较大的内存，在setting.py的以下注释用于设置缓存

#HTTPCACHE_ENABLED = True

#HTTPCACHE_EXPIRATION_SECS = 0

#HTTPCACHE_DIR = ‘httpcache’

#HTTPCACHE_IGNORE_HTTP_CODES = []

#HTTPCACHE_STORAGE = ‘scrapy.extensions.httpcache.FilesystemCacheStorage’