Scrapy 刮擦/飞溅选择选项

我真的开始对“刮擦飞溅”的工作原理感到沮丧。我不知道如何选择一个值，并在选择值后截图。这是我到目前为止不起作用的代码

抓取url：

选择了大，但我想在本例中选择小，然后截图

import scrapy
from scrapy_splash import SplashRequest, SplashFormRequest
from scrapy import FormRequest, Selector


class QuotesSpider(scrapy.Spider):
    name = "quotes"

    def start_requests(self):
        urls = [
            'https://www.chewy.com/kong-classic-dog-toy-large/dp/38485',
        ]
        for url in urls:
            yield scrapy.Request(url=url, callback=self.parse)

    # Gets HTML and saves to file
    def parse(self, response):
        page = response.url.split("/")[-2]
        filename = 'quotes-%s.html' % page
        with open(filename, 'wb') as f:
            f.write(response.body)
        self.log('Saved file %s' % filename)

        yield FormRequest.from_response(
            response,
            formname='sku-selector',
            formdata={
                '15949': 'Small', 
            }
        )

        with open('request.png', 'wb') as f:
            f.write(response.body)

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您在哪里使用SplashRequest？我不知道我在使用什么：(