Flask中集成Scrapy

如果只是在Flask中调用Scrapy爬虫,可能会遇到如下错误:

ValueError: signal only works in main thread
# 或者
twisted.internet.error.ReactorNotRestartable

解决的办法有几个。

1 使用python子进程(subproccess)

首先,确保目录结构类似如下:

> tree -L 1                                                                                                                                                              

├── dirbot
├── README.rst
├── scrapy.cfg
├── server.py
└── setup.py

然后在,新进程中启动爬虫:

# server.py
import subprocess

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
    """
    Run spider in another process and store items in file. Simply issue command:

    > scrapy crawl dmoz -o "output.json"

    wait for  this command to finish, and read output.json to client.
    """
    spider_name = "dmoz"
    subprocess.check_output(['scrapy', 'crawl', spider_name, "-o", "output.json"])
    with open("output.json") as items_file:
        return items_file.read()

if __name__ == '__main__':
    app.run(debug=True)

新进程中启动爬虫:

2 使用Twisted-Klein + Scrapy

代码如下:

# server.py
import json

from klein import route, run
from scrapy import signals
from scrapy.crawler import CrawlerRunner

from dirbot.spiders.dmoz import DmozSpider


class MyCrawlerRunner(CrawlerRunner):
    """
    Crawler object that collects items and returns output after finishing crawl.
    """
    def crawl(self, crawler_or_spidercls, *args, **kwargs):
        # keep all items scraped
        self.items = []

        # create crawler (Same as in base CrawlerProcess)
        crawler = self.create_crawler(crawler_or_spidercls)

        # handle each item scraped
        crawler.signals.connect(self.item_scraped, signals.item_scraped)

        # create Twisted.Deferred launching crawl
        dfd = self._crawl(crawler, *args, **kwargs)

        # add callback - when crawl is done cal return_items
        dfd.addCallback(self.return_items)
        return dfd

    def item_scraped(self, item, response, spider):
        self.items.append(item)

    def return_items(self, result):
        return self.items


def return_spider_output(output):
    """
    :param output: items scraped by CrawlerRunner
    :return: json with list of items
    """
    # this just turns items into dictionaries
    # you may want to use Scrapy JSON serializer here
    return json.dumps([dict(item) for item in output])


@route("/")
def schedule(request):
    runner = MyCrawlerRunner()
    spider = DmozSpider()
    deferred = runner.crawl(spider)
    deferred.addCallback(return_spider_output)
    return deferred


run("localhost", 8080)

3 使用ScrapyRT

安装ScrapyRT,然后启动:

> scrapyrt 

文章来源:https://stackoverflow.com/questions/36384286/how-to-integrate-flask-scrapy

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