# When you run the Scrapy crawler from a program, the code blocks until the Scrapy crawler is finished. This is due to how Twisted (the underlying asynchronous network library) works. This prevents using the Scrapy crawler from scripts or other code.
# 
# To circumvent this issue you can run the Scrapy crawler in a thread with this code.
# 
# Keep in mind that this code is mainly for illustrative purposes and far from production ready.
# 
# Also the code was only tested with Scrapy 0.8, and will probably need some adjustments for newer versions (since the core API isn't stable yet), but you get the idea.
 
"""
Code to run Scrapy crawler in a thread - works on Scrapy 0.8
"""
 
import threading, Queue
 
from twisted.internet import reactor
 
from scrapy.xlib.pydispatch import dispatcher
from scrapy.core.manager import scrapymanager
from scrapy.core.engine import scrapyengine
from scrapy.core import signals
 
class CrawlerThread(threading.Thread):
 
    def __init__(self): 
        threading.Thread.__init__(self)
        self.running = False
 
    def run(self):
        self.running = True
        scrapymanager.configure(control_reactor=False)
        scrapymanager.start()
        reactor.run(installSignalHandlers=False)
 
    def crawl(self, *args):
        if not self.running:
            raise RuntimeError("CrawlerThread not running")
        self._call_and_block_until_signal(signals.spider_closed, \
            scrapymanager.crawl, *args)
 
    def stop(self):
        reactor.callFromThread(scrapyengine.stop)
 
    def _call_and_block_until_signal(self, signal, f, *a, **kw):
        q = Queue.Queue()
        def unblock():
            q.put(None)
        dispatcher.connect(unblock, signal=signal)
        reactor.callFromThread(f, *a, **kw)
        q.get()
 
 
# Usage example below:
 
import os
os.environ.setdefault('SCRAPY_SETTINGS_MODULE', 'myproject.settings')
 
from scrapy.xlib.pydispatch import dispatcher
from scrapy.core import signals
from scrapy.conf import settings
from scrapy.crawler import CrawlerThread
 
settings.overrides['LOG_ENABLED'] = False # avoid log noise
 
def item_passed(item):
    print "Just scraped item:", item
 
dispatcher.connect(item_passed, signal=signals.item_passed)
 
crawler = CrawlerThread()
print "Starting crawler thread..."
crawler.start()
print "Crawling somedomain.com...."
crawler.crawl('somedomain.com) # blocking call
print "Crawling anotherdomain.com..."
crawler.crawl('anotherdomain.com') # blocking call
print "Stopping crawler thread..."
crawler.stop()
 
# Snippet imported from snippets.scrapy.org (which no longer works)
# author: pablo
# date  : Aug 11, 2010