scrapy奇技淫巧1

Request传递值到callback回调函数

def parse(self, response):
    request = scrapy.Request('http://www.example.com/index.html',
                             callback=self.parse_page2,
                             cb_kwargs=dict(main_url=response.url))
    request.cb_kwargs['foo'] = 'bar'  # add more arguments for the callback
    yield request

def parse_page2(self, response, main_url, foo):
    yield dict(
        main_url=main_url,
        other_url=response.url,
        foo=foo,
    )

Request传递cookie并且指定在一定范围的域名内存储接下来获得的cookie.

request_with_cookies = Request(url="http://www.example.com",
                               cookies=[{'name': 'currency',
                                        'value': 'USD',
                                        'domain': 'example.com',
                                        'path': '/currency'}])

自定义domain\path属性，可以实现——自动存储在这些网页中获得的cookie并自动加上，以后不用手动添加。如果网站要cookie才能进，表示只需要在开头发送一次就可以了。

把Request的dont_filter设置为True,可以防止它被反重复机制过滤，可以用在当想要对同一页面多此请求。Default to False.

使用Request的errback来捕获异常。

import scrapy

from scrapy.spidermiddlewares.httperror import HttpError
from twisted.internet.error import DNSLookupError
from twisted.internet.error import TimeoutError, TCPTimedOutError

class ErrbackSpider(scrapy.Spider):
    name = "errback_example"
    start_urls = [
        "http://www.httpbin.org/",              # HTTP 200 expected
        "http://www.httpbin.org/status/404",    # Not found error
        "http://www.httpbin.org/status/500",    # server issue
        "http://www.httpbin.org:12345/",        # non-responding host, timeout expected
        "http://www.httphttpbinbin.org/",       # DNS error expected
    ]

    def start_requests(self):
        for u in self.start_urls:
            yield scrapy.Request(u, callback=self.parse_httpbin,
                                    errback=self.errback_httpbin,
                                    dont_filter=True)

    def parse_httpbin(self, response):
        self.logger.info('Got successful response from {}'.format(response.url))
        # do something useful here...

    def errback_httpbin(self, failure):
        # log all failures
        self.logger.error(repr(failure))

        # in case you want to do something special for some errors,
        # you may need the failure's type:

        if failure.check(HttpError):
            # these exceptions come from HttpError spider middleware
            # you can get the non-200 response
            response = failure.value.response
            self.logger.error('HttpError on %s', response.url)

        elif failure.check(DNSLookupError):
            # this is the original request
            request = failure.request
            self.logger.error('DNSLookupError on %s', request.url)

        elif failure.check(TimeoutError, TCPTimedOutError):
            request = failure.request
            self.logger.error('TimeoutError on %s', request.url)

使用Request的replace方法构建一个新的Request，除了重新定义的值，其他的照搬原来的值。

replace([url, method, headers, body, cookies, meta, flags, encoding, priority, dont_filter, callback, errback, cb_kwargs])

返回具有相同成员的Request对象，但那些通过指定关键字参数赋予新值的成员除外。默认情况下，Request.cb_kwargs和Request.meta属性是浅复制的（除非给定新值作为参数）。

scrapy.FormRequest和scrapy.FormRequest.from_response   https://blog.csdn.net/qq_33472765/article/details/80958820

具体可查看文档。from_response和FromRequest不同，后者是单纯的post，前者是与填充html页面的form字段，可以自己指定表单的位置（如果有多个），在模拟点击。如果是那些javascript的表单，也可以指定不模拟点击。

return [FormRequest(url="http://www.example.com/post/action",
                    formdata={'name': 'John Doe', 'age': '27'},
                    callback=self.after_post)]

网站通常会通过<input type =“ hidden”>元素（例如，与会话相关的数据或身份验证令牌（用于登录页面））提供预先填充的表单字段。抓取时，您会希望自动填充这些字段，并且仅覆盖其中的几个字段，例如用户名和密码。您可以将FormRequest.from_response（）方法用于此作业。

import scrapy

def authentication_failed(response):
    # TODO: Check the contents of the response and return True if it failed
    # or False if it succeeded.
    pass

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):
        if authentication_failed(response):
            self.logger.error("Login failed")
            return

        # continue scraping with authenticated session...