scrapy 登录

说明：
本文参考了官网文档，以及stackoverflow的几个问题

注意：
下面这个爬虫不能实际运行！我只是用它来展示登录，以及之后如何处理。

方式一：FormRequest

import scrapy

from myprojct.items import ExampleItem

class ExampleSpider(scrapy.Spider):
    name = 'example'
    allowed_domains = ["example.com"]
    
    start_urls = [
        'http://www.example.com/articals/',
        'http://www.example.com/blogs/',
        'http://www.example.com/news/',
    ]

    # 先登录
    def start_requests(self):
        return [scrapy.FormRequest("http://www.example.com/login",
                                   formdata={'user': 'john', 'pass': 'secret'},
                                   callback=self.login_check)]
    
    # 检查登录。
    def login_check(self, response):
        if "Login failed" not in response.body: # 如果登录成功，则
            for url in self.start_urls:
                yield scrapy.Request(url, callback=self.parse_page)
    
    # 解析页面
    def parse_page(self, response):
        for tablerow in response.css('table.basictable tr'):
            item = ExampleItem()
            item["name"] = tablerow.xpath('td[1]').extract()
            item["handicap"] = tablerow.xpath('td[2]').extract()
            item["exact"] = tablerow.xpath('td[3]').extract()
            item["category"] = tablerow.xpath('td[4]').extract()
            yield item
        

方式二：FormRequest.from_response

import scrapy

class LoginSpider(scrapy.Spider):
    name = 'example.com'
    start_urls = ['http://www.example.com/users/login.php']

    def parse(self, response):
        return scrapy.FormRequest.from_response(
            response,
            formdata={'username': 'john', 'password': 'secret'},
            callback=self.after_login
        )

    def after_login(self, response):
        # check login succeed before going on
        if "authentication failed" in response.body:
            self.logger.error("Login failed")
            return

        # continue scraping with authenticated session...