如何使用scrapy捕捉错误，以便在收到用户超时错误时可以执行某些操作？

Question

ERROR: Error downloading <GET URL_HERE>: User timeout caused connection failure.

我使用刮刀时不时会遇到这个问题。有没有方法可以抓住这个问题并在它发生时运行函数？我在网上找不到怎么做。

Answer 1

我更喜欢使用这样的自定义重试中间件：

from scrapy.contrib.downloadermiddleware.retry import RetryMiddleware

from fake_useragent import FakeUserAgentError

class FakeUserAgentErrorRetryMiddleware(RetryMiddleware):

    def process_exception(self, request, exception, spider):
        if type(exception) == FakeUserAgentError: return self._retry(request, exception, spider)

Answer 2

您可以在Request实例中定义^{}：

errback (callable) – a function that will be called if any exception was raised while processing the request. This includes pages that failed with 404 HTTP errors and such. It receives a Twisted Failure instance as first parameter.

下面是一些示例代码（用于scrapy 1.0），您可以使用：

# -*- coding: utf-8 -*-
# errbacks.py
import scrapy

# from scrapy.contrib.spidermiddleware.httperror import HttpError
from scrapy.spidermiddlewares.httperror import HttpError
from twisted.internet.error import DNSLookupError
from twisted.internet.error import TimeoutError


class ErrbackSpider(scrapy.Spider):
    name = "errbacks"
    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.error('Got successful response from {}'.format(response.url))
        # do something useful now

    def errback_httpbin(self, failure):
        # log all errback failures,
        # in case you want to do something special for some errors,
        # you may need the failure's type
        self.logger.error(repr(failure))

        #if isinstance(failure.value, HttpError):
        if failure.check(HttpError):
            # you can get the response
            response = failure.value.response
            self.logger.error('HttpError on %s', response.url)

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

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

以及scrapy shell中的输出（仅1次重试，5秒下载超时）：

$ scrapy runspider errbacks.py --set DOWNLOAD_TIMEOUT=5 --set RETRY_TIMES=1
2015-06-30 23:45:55 [scrapy] INFO: Scrapy 1.0.0 started (bot: scrapybot)
2015-06-30 23:45:55 [scrapy] INFO: Optional features available: ssl, http11
2015-06-30 23:45:55 [scrapy] INFO: Overridden settings: {'DOWNLOAD_TIMEOUT': '5', 'RETRY_TIMES': '1'}
2015-06-30 23:45:56 [scrapy] INFO: Enabled extensions: CloseSpider, TelnetConsole, LogStats, CoreStats, SpiderState
2015-06-30 23:45:56 [scrapy] INFO: Enabled downloader middlewares: HttpAuthMiddleware, DownloadTimeoutMiddleware, UserAgentMiddleware, RetryMiddleware, DefaultHeadersMiddleware, MetaRefreshMiddleware, HttpCompressionMiddleware, RedirectMiddleware, CookiesMiddleware, ChunkedTransferMiddleware, DownloaderStats
2015-06-30 23:45:56 [scrapy] INFO: Enabled spider middlewares: HttpErrorMiddleware, OffsiteMiddleware, RefererMiddleware, UrlLengthMiddleware, DepthMiddleware
2015-06-30 23:45:56 [scrapy] INFO: Enabled item pipelines: 
2015-06-30 23:45:56 [scrapy] INFO: Spider opened
2015-06-30 23:45:56 [scrapy] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)
2015-06-30 23:45:56 [scrapy] DEBUG: Telnet console listening on 127.0.0.1:6023
2015-06-30 23:45:56 [scrapy] DEBUG: Retrying <GET http://www.httphttpbinbin.org/> (failed 1 times): DNS lookup failed: address 'www.httphttpbinbin.org' not found: [Errno -5] No address associated with hostname.
2015-06-30 23:45:56 [scrapy] DEBUG: Gave up retrying <GET http://www.httphttpbinbin.org/> (failed 2 times): DNS lookup failed: address 'www.httphttpbinbin.org' not found: [Errno -5] No address associated with hostname.
2015-06-30 23:45:56 [errbacks] ERROR: <twisted.python.failure.Failure <class 'twisted.internet.error.DNSLookupError'>>
2015-06-30 23:45:56 [errbacks] ERROR: DNSLookupError on http://www.httphttpbinbin.org/
2015-06-30 23:45:56 [scrapy] DEBUG: Crawled (200) <GET http://www.httpbin.org/> (referer: None)
2015-06-30 23:45:56 [scrapy] DEBUG: Crawled (404) <GET http://www.httpbin.org/status/404> (referer: None)
2015-06-30 23:45:56 [errbacks] ERROR: Got successful response from http://www.httpbin.org/
2015-06-30 23:45:56 [errbacks] ERROR: <twisted.python.failure.Failure <class 'scrapy.spidermiddlewares.httperror.HttpError'>>
2015-06-30 23:45:56 [errbacks] ERROR: HttpError on http://www.httpbin.org/status/404
2015-06-30 23:45:56 [scrapy] DEBUG: Retrying <GET http://www.httpbin.org/status/500> (failed 1 times): 500 Internal Server Error
2015-06-30 23:45:57 [scrapy] DEBUG: Gave up retrying <GET http://www.httpbin.org/status/500> (failed 2 times): 500 Internal Server Error
2015-06-30 23:45:57 [scrapy] DEBUG: Crawled (500) <GET http://www.httpbin.org/status/500> (referer: None)
2015-06-30 23:45:57 [errbacks] ERROR: <twisted.python.failure.Failure <class 'scrapy.spidermiddlewares.httperror.HttpError'>>
2015-06-30 23:45:57 [errbacks] ERROR: HttpError on http://www.httpbin.org/status/500
2015-06-30 23:46:01 [scrapy] DEBUG: Retrying <GET http://www.httpbin.org:12345/> (failed 1 times): User timeout caused connection failure.
2015-06-30 23:46:06 [scrapy] DEBUG: Gave up retrying <GET http://www.httpbin.org:12345/> (failed 2 times): User timeout caused connection failure.
2015-06-30 23:46:06 [errbacks] ERROR: <twisted.python.failure.Failure <class 'twisted.internet.error.TimeoutError'>>
2015-06-30 23:46:06 [errbacks] ERROR: TimeoutError on http://www.httpbin.org:12345/
2015-06-30 23:46:06 [scrapy] INFO: Closing spider (finished)
2015-06-30 23:46:06 [scrapy] INFO: Dumping Scrapy stats:
{'downloader/exception_count': 4,
 'downloader/exception_type_count/twisted.internet.error.DNSLookupError': 2,
 'downloader/exception_type_count/twisted.internet.error.TimeoutError': 2,
 'downloader/request_bytes': 1748,
 'downloader/request_count': 8,
 'downloader/request_method_count/GET': 8,
 'downloader/response_bytes': 12506,
 'downloader/response_count': 4,
 'downloader/response_status_count/200': 1,
 'downloader/response_status_count/404': 1,
 'downloader/response_status_count/500': 2,
 'finish_reason': 'finished',
 'finish_time': datetime.datetime(2015, 6, 30, 21, 46, 6, 537191),
 'log_count/DEBUG': 10,
 'log_count/ERROR': 9,
 'log_count/INFO': 7,
 'response_received_count': 3,
 'scheduler/dequeued': 8,
 'scheduler/dequeued/memory': 8,
 'scheduler/enqueued': 8,
 'scheduler/enqueued/memory': 8,
 'start_time': datetime.datetime(2015, 6, 30, 21, 45, 56, 322235)}
2015-06-30 23:46:06 [scrapy] INFO: Spider closed (finished)

注意scrapy如何在其统计信息中记录异常：

'downloader/exception_type_count/twisted.internet.error.DNSLookupError': 2,
'downloader/exception_type_count/twisted.internet.error.TimeoutError': 2,