如何以编程方式计划Scrapy爬网执行

Question

我想创建一个调度程序脚本，以在一个序列中多次运行同一蜘蛛。

到目前为止，我得到了以下内容：

#!/usr/bin/python3
"""Scheduler for spiders."""
import time

from scrapy.crawler import CrawlerProcess
from scrapy.utils.project import get_project_settings

from my_project.spiders.deals import DealsSpider


def crawl_job():
    """Job to start spiders."""
    settings = get_project_settings()
    process = CrawlerProcess(settings)
    process.crawl(DealsSpider)
    process.start() # the script will block here until the end of the crawl


if __name__ == '__main__':

    while True:
        crawl_job()
        time.sleep(30) # wait 30 seconds then crawl again

目前，蜘蛛网第一次正常执行，然后经过一段时间的延迟，蜘蛛网再次启动，但是就在它开始抓取之前，我收到以下错误消息：

Traceback (most recent call last):
  File "scheduler.py", line 27, in <module>
    crawl_job()
  File "scheduler.py", line 17, in crawl_job
    process.start() # the script will block here until the end of the crawl
  File "/usr/local/lib/python3.5/dist-packages/scrapy/crawler.py", line 285, in start
    reactor.run(installSignalHandlers=False)  # blocking call
  File "/usr/local/lib/python3.5/dist-packages/twisted/internet/base.py", line 1193, in run
    self.startRunning(installSignalHandlers=installSignalHandlers)
  File "/usr/local/lib/python3.5/dist-packages/twisted/internet/base.py", line 1173, in startRunning
    ReactorBase.startRunning(self)
  File "/usr/local/lib/python3.5/dist-packages/twisted/internet/base.py", line 684, in startRunning
    raise error.ReactorNotRestartable()
twisted.internet.error.ReactorNotRestartable

不幸的是，我不熟悉该Twisted框架及其框架Reactor，因此不胜感激！

Answer 1

您收到ReactorNotRestartable错误消息是因为Reactor无法在Twisted中多次启动。基本上，每次process.start()调用时，它将尝试启动反应堆。网络上有很多与此有关的信息。这是一个简单的解决方案：

from twisted.internet import reactor
from scrapy.crawler import CrawlerRunner
from scrapy.utils.project import get_project_settings

from my_project.spiders.deals import DealsSpider


def crawl_job():
    """
    Job to start spiders.
    Return Deferred, which will execute after crawl has completed.
    """
    settings = get_project_settings()
    runner = CrawlerRunner(settings)
    return runner.crawl(DealsSpider)

def schedule_next_crawl(null, sleep_time):
    """
    Schedule the next crawl
    """
    reactor.callLater(sleep_time, crawl)

def crawl():
    """
    A "recursive" function that schedules a crawl 30 seconds after
    each successful crawl.
    """
    # crawl_job() returns a Deferred
    d = crawl_job()
    # call schedule_next_crawl(<scrapy response>, n) after crawl job is complete
    d.addCallback(schedule_next_crawl, 30)
    d.addErrback(catch_error)

def catch_error(failure):
    print(failure.value)

if __name__=="__main__":
    crawl()
    reactor.run()

您的代码段有一些明显的不同。的reactor直接调用，替换CrawlerProcess为CrawlerRunner，time.sleep已被移除，以使反应器中不会阻塞，该while环已经被替换为连续的调用crawl经由功能callLater。它很短，应该做您想要的。如果有任何部分使您感到困惑，请告诉我，我将详细说明。

更新-在特定时间抓取

import datetime as dt

def schedule_next_crawl(null, hour, minute):
    tomorrow = (
        dt.datetime.now() + dt.timedelta(days=1)
        ).replace(hour=hour, minute=minute, second=0, microsecond=0)
    sleep_time = (tomorrow - dt.datetime.now()).total_seconds()
    reactor.callLater(sleep_time, crawl)

def crawl():
    d = crawl_job()
    # crawl everyday at 1pm
    d.addCallback(schedule_next_crawl, hour=13, minute=30)