scrapy-redis代码研究
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README.rst

说在前面

此repository fork自scrapy-redis,在此基础上,做了如下更改:

  • 重写部分代码,与更新版本的scrapy兼容。
  • 更清晰的展现分布式例程的实现。
  • 用法的翻译/代码原理研究/注释翻译。

注意:部分兼容性问题存在于此库中,关于此方面问题可直接查看源代码库 (github.com/darkrho/scrapy-redis)或者 (github.com/younghz/scrapy-redis)。

新例程原理与使用

关于新例程 "example-project-by-younghz" 实现 原理使用 请参见本repo的wiki, 或者查看我的这篇文章(http://blog.csdn.net/u012150179/article/details/38091411)。在例程文件夹下也有README文件。

最近有人发邮件问我相关问题,在上面指出的文章中都有详细说明。

Redis-based components for Scrapy

This project attempts to provide Redis-backed components for Scrapy.

Features:

  • 分布式爬取/抓取

    可以同时实例化多个spider,它们使用同一个redis队列(request queue)。 适合广度多域名的抓取。

  • 分布式post-processing(处理得到的item)

    可以将抓取的item放进redis队列中,这样你就可以在需要的时候在item队列中进行处理。

Requirements:

  • Scrapy >= 0.14
  • redis-py (tested on 2.4.9)
  • redis server (tested on 2.4-2.6)

Available Scrapy components:

  • Scheduler
  • Duplication Filter
  • Item Pipeline
  • Base Spider

Installation

From pypi:

$ pip install scrapy-redis

From github:

$ git clone https://github.com/darkrho/scrapy-redis.git
$ cd scrapy-redis
$ python setup.py install

使用

Enable the components in your settings.py:

# Enables scheduling storing requests queue in redis.
SCHEDULER = "scrapy_redis.scheduler.Scheduler"

# Don't cleanup redis queues, allows to pause/resume crawls.
SCHEDULER_PERSIST = True

# Schedule requests using a priority queue. (default)
SCHEDULER_QUEUE_CLASS = 'scrapy_redis.queue.SpiderPriorityQueue'

# Schedule requests using a queue (FIFO).
SCHEDULER_QUEUE_CLASS = 'scrapy_redis.queue.SpiderQueue'

# Schedule requests using a stack (LIFO).
SCHEDULER_QUEUE_CLASS = 'scrapy_redis.queue.SpiderStack'

# Max idle time to prevent the spider from being closed when distributed crawling.
# This only works if queue class is SpiderQueue or SpiderStack,
# and may also block the same time when your spider start at the first time (because the queue is empty).
SCHEDULER_IDLE_BEFORE_CLOSE = 10

# Store scraped item in redis for post-processing.
ITEM_PIPELINES = [
    'scrapy_redis.pipelines.RedisPipeline',
]

# Specify the host and port to use when connecting to Redis (optional).
REDIS_HOST = 'localhost'
REDIS_PORT = 6379

# Specify the full Redis URL for connecting (optional).
# If set, this takes precedence over the REDIS_HOST and REDIS_PORT settings.
REDIS_URL = 'redis://user:pass@hostname:9001'

Note

Version 0.3 changed the requests serialization from marshal to cPickle, therefore persisted requests using version 0.2 will not able to work on 0.3.

Running the example project

这个例子所表现的是多个crawler怎样使用一个spider的request queue。

  1. 安装scrapy-redis。

  2. 运行crawler然后停止:

    $ cd example-project
    $ scrapy crawl dmoz
    ... [dmoz] ...
    ^C
    
  3. 再次运行crawler从上次停止位置恢复:

    $ scrapy crawl dmoz
    ... [dmoz] DEBUG: Resuming crawl (9019 requests scheduled)
    
  4. 运行更多的scrapy crawlers:

    $ scrapy crawl dmoz
    ... [dmoz] DEBUG: Resuming crawl (8712 requests scheduled)
    
  5. 运行一个或更多的post-processing workers:

    $ python process_items.py
    Processing: Kilani Giftware (http://www.dmoz.org/Computers/Shopping/Gifts/)
    Processing: NinjaGizmos.com (http://www.dmoz.org/Computers/Shopping/Gifts/)
    ...
    

Feeding a spider from Redis

`scrapy_redis.spiders.RedisSpider`类可以使spider从redis中读取urls, redis queue中的urls会被依次处理,如果第一个request yeilds更多的request, 那么spider会首先处理这些request,然后在从redis fetch 另外的url。

For example, create a file myspider.py with the code below:

from scrapy_redis.spiders import RedisSpider

class MySpider(RedisSpider):
    name = 'myspider'

    def parse(self, response):
        # do stuff
        pass

然后:

  1. 运行spider:

    scrapy runspider myspider.py
    
  2. push urls to redis:

    redis-cli lpush myspider:start_urls http://google.com
    

Changelog

0.5
  • Added REDIS_URL setting to support Redis connection string.
  • Added SCHEDULER_IDLE_BEFORE_CLOSE setting to prevent the spider closing too quickly when the queue is empty. Default value is zero keeping the previous behavior.
0.4
  • Added RedisSpider and RedisMixin classes as building blocks for spiders to be fed through a redis queue.
  • Added redis queue stats.
  • Let the encoder handle the item as it comes instead converting it to a dict.
0.3
  • Added support for different queue classes.
  • Changed requests serialization from marshal to cPickle.
0.2
  • Improved backward compatibility.
  • Added example project.
0.1
  • Initial version.
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