在scrapy中使用ItemLoader将缺省值设置为None的KeyError处理

from scrapy.loader import ItemLoader
from scrapy import Item

class MyItem(Item):
    field1 = scrapy.Field()
    field2 = scrapy.Field()
    # 其他字段...

class MyItemLoader(ItemLoader):
    default_item_class = MyItem

from myproject.items import MyItem, MyItemLoader

class MySpider(scrapy.Spider):
    name = 'myspider'
    start_urls = ['http://example.com']

    def parse(self, response):
        loader = MyItemLoader(item=MyItem(), response=response)
        loader.add_xpath('field1', '//div[@class="field1"]/text()')
        loader.add_xpath('field2', '//div[@class="field2"]/text()')
        # 添加其他字段...

        item = loader.load_item()
        yield item