CODEWITHSUNDEEP
pythonflaskscrapyreactortwisted.internet
sagar
sagar

Reputation: 745

Python scrapy ReactorNotRestartable substitute

I have been trying to make an app in Python using Scrapy that has the following functionality:

I am able to do this using the following code:

items = []
def add_item(item):
    items.append(item)

# set up crawler
crawler = Crawler(SpiderClass,settings=get_project_settings())
crawler.signals.connect(add_item, signal=signals.item_passed)

# This is added to make the reactor stop, if I don't use this, the code stucks at reactor.run() line.
crawler.signals.connect(reactor.stop, signal=signals.spider_closed) #@UndefinedVariable 
crawler.crawl(requestParams=requestParams)
# start crawling 
reactor.run() #@UndefinedVariable
return str(items)

Now the problem I am facing is after making the reactor stop (which seems necessary to me since I don't want to stuck to the reactor.run()). I couldn't accept the further request after first request. After first request gets completed, I got the following error:

Traceback (most recent call last):
  File "c:\python27\lib\site-packages\flask\app.py", line 1988, in wsgi_app
    response = self.full_dispatch_request()
  File "c:\python27\lib\site-packages\flask\app.py", line 1641, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "c:\python27\lib\site-packages\flask\app.py", line 1544, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "c:\python27\lib\site-packages\flask\app.py", line 1639, in full_dispatch_request
    rv = self.dispatch_request()
  File "c:\python27\lib\site-packages\flask\app.py", line 1625, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "F:\my_workspace\jobvite\jobvite\com\jobvite\web\RequestListener.py", line 38, in submitForm
    reactor.run() #@UndefinedVariable
  File "c:\python27\lib\site-packages\twisted\internet\base.py", line 1193, in run
    self.startRunning(installSignalHandlers=installSignalHandlers)
  File "c:\python27\lib\site-packages\twisted\internet\base.py", line 1173, in startRunning
    ReactorBase.startRunning(self)
  File "c:\python27\lib\site-packages\twisted\internet\base.py", line 684, in startRunning
    raise error.ReactorNotRestartable()
ReactorNotRestartable

Which is obvious, since we can not restart the reactor.

So my questions are:

1) How could I provide support for the next requests to crawl?

2) Is there any way to move to next line after reactor.run() without stopping it?

Upvotes: 8

Views: 1003

Answers (2)

Dinesh Agrawal
Dinesh Agrawal

Reputation: 346

Here is a simple solution to your problem

from flask import Flask
import threading
import subprocess
import sys
app = Flask(__name__) 

class myThread (threading.Thread):
    def __init__(self,target):
        threading.Thread.__init__(self)
        self.target = target
    def run(self):
        start_crawl()

def start_crawl():
    pid = subprocess.Popen([sys.executable, "start_request.py"])
    return


@app.route("/crawler/start") 
def start_req():
    print ":request"
    threadObj = myThread("run_crawler")
    threadObj.start()
    return "Your crawler is in running state" 
if (__name__ == "__main__"): 
    app.run(port = 5000)

In the above solution I assume that you are able to start your crawler from command line using command start_request.py file on shell/command line.

Now what we are doing is using threading in python to launch a new thread for each incoming request. Now you can easily able to run your crawler instance in parallel for each hit. Just control your number of threads using threading.activeCount()

Upvotes: 1

Evhz
Evhz

Reputation: 9246

I recommend you using a queue system like Rq (for simplicity, but there are few others).
You could have a craw function:

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

from spiders import MySpider

def runCrawler(url, keys, mode, outside, uniqueid): 

    runner = CrawlerRunner( get_project_settings() )

    d = runner.crawl( MySpider, url=url, param1=value1, ... )

    d.addBoth(lambda _: reactor.stop())
    reactor.run()

Then in your main code, use the Rq queue in order to collect crawler executions:

# other imports
pool = redis.ConnectionPool( host=REDIS_HOST, port=REDIS_PORT, db=your_redis_db_number)
redis_conn =redis.Redis(connection_pool=pool)  

q = Queue('parse', connection=redis_conn)

# urlSet is a list of http:// or https:// like url's
for url in urlSet:
    job = q.enqueue(runCrawler, url, param1, ... , timeout=600 )

Do not forget to start a rq worker process, working for the same queue name (here parse). For example, execute in a terminal session:

rq worker parse

Upvotes: 1

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