Question

I need to create a user configurable web spider/crawler, and I’m thinking about using Scrapy. But, I can’t hard-code the domains and allowed URL regex:es — this will instead be configurable in a GUI.

How do I (as simple as possible) create a spider or a set of spiders with Scrapy where the domains and allowed URL regex:es are dynamically configurable? E.g. I write the configuration to a file, and the spider reads it somehow.

Answer 1

WARNING: This answer was for Scrapy v0.7, spider manager api changed a lot since then.

Override default SpiderManager class, load your custom rules from a database or somewhere else and instanciate a custom spider with your own rules/regexes and domain_name

in mybot/settings.py:

SPIDER_MANAGER_CLASS = 'mybot.spidermanager.MySpiderManager'

in mybot/spidermanager.py:

from mybot.spider import MyParametrizedSpider

class MySpiderManager(object):
    loaded = True

    def fromdomain(self, name):
        start_urls, extra_domain_names, regexes = self._get_spider_info(name)
        return MyParametrizedSpider(name, start_urls, extra_domain_names, regexes)

    def close_spider(self, spider):
        # Put here code you want to run before spiders is closed
        pass

    def _get_spider_info(self, name):
        # query your backend (maybe a sqldb) using `name` as primary key, 
        # and return start_urls, extra_domains and regexes
        ...
        return (start_urls, extra_domains, regexes)

and now your custom spider class, in mybot/spider.py:

from scrapy.spider import BaseSpider

class MyParametrizedSpider(BaseSpider):

    def __init__(self, name, start_urls, extra_domain_names, regexes):
        self.domain_name = name
        self.start_urls = start_urls
        self.extra_domain_names = extra_domain_names
        self.regexes = regexes

     def parse(self, response):
         ...

Notes:

• You can extend CrawlSpider too if you want to take advantage of its Rules system
• To run a spider use: ./scrapy-ctl.py crawl <name>, where name is passed to SpiderManager.fromdomain and is the key to retreive more spider info from the backend system
• As solution overrides default SpiderManager, coding a classic spider (a python module per SPIDER) doesn’t works, but, I think this is not an issue for you. More info on default spiders manager TwistedPluginSpiderManager