Python 和 Scrapy 引用项目的属性

Question

在 Scrapy 的教程网站上，他们有一个项目的代码。

import scrapy

class DmozItem(scrapy.Item):
    title = scrapy.Field()
    link = scrapy.Field()
    desc = scrapy.Field()

然后他们就有了蜘蛛的代码。

import scrapy

from tutorial.items import DmozItem

class DmozSpider(scrapy.Spider):
    name = "dmoz"
    allowed_domains = ["dmoz.org"]
    start_urls = [
        "http://www.dmoz.org/Computers/Programming/Languages/Python/Books/",
        "http://www.dmoz.org/Computers/Programming/Languages/Python/Resources/"
    ]

    def parse(self, response):
        for sel in response.xpath('//ul/li'):
            item = DmozItem()
            item['title'] = sel.xpath('a/text()').extract()
            item['link'] = sel.xpath('a/@href').extract()
            item['desc'] = sel.xpath('text()').extract()
            yield item

我的问题是为什么他们可以使用 [] 括号引用项目的标题？我认为当你引用一个变量时，它会是 item.title = another 。我有什么遗漏的吗？

Answer 1

这是因为 Scrapy 在底层使用 UserDict.DictMixin mixin 为 Item类:

class UserDict.DictMixin

Mixin defining all dictionary methods for classes that already have a minimum dictionary interface including __getitem__(), __setitem__(), __delitem__(), and keys().

此外，引用 Scrapy 的 documentation :

Item objects are simple containers used to collect the scraped data. They provide a dictionary-like API with a convenient syntax for declaring their available fields.

另请参阅the actual implementation .