from scrapy import Spider
from selenium import webdriver
from scrapy.selector import Selector
from scrapy.http import Request

from selenium.webdriver.chrome.service import Service
from selenium.webdriver.chrome.options import Options

class BookSeleniumSpider(Spider):
    name = 'book_selenium'
    allowed_domains = ['books.toscrape.com']

    def start_req(self):
        s = Service('C:\\Users\\aps\\Documents\\chromedriver.exe')
        chrome_options = webdriver.ChromeOptions()
        chrome_options.add_argument('--no-sandbox')
        self.driver = webdriver.Chrome(service=s, chrome_options=chrome_options)

        # Get the site we want to start scraping
        self.driver.get('http://books.toscrape.com')

        sel = Selector(text=self.driver.page_source)
        books = sel.xpath('//h3/a/@href').extract()

        for book in books:
            url = 'http://books.toscrape.com/' + book
            print(url)

    def parse_book(self, response):
        pass

当我把parse函数改为start_req时，它停止工作了。但是当我把它改回parse时，它工作得很好。我不知道为什么。有人能给我解释一下吗