scrapy-redis使用以及剖析

 scrapy-redis是一个基于redis的scrapy组件,通过它可以快速实现简单分布式爬虫程序,该组件本质上提供了三大功能:
  • scheduler - 调度器
  • dupefilter - URL去重规则(被调度器使用)
  • pipeline   - 数据持久化

scrapy-redis组件

1. URL去重

定义去重规则(被调度器调用并应用)

    a. 内部会使用以下配置进行连接Redis

        # REDIS_HOST = 'localhost'                            # 主机名
        # REDIS_PORT = 6379                                   # 端口
        # REDIS_URL = 'redis://user:pass@hostname:9001'       # 连接URL(优先于以上配置)
        # REDIS_PARAMS  = {}                                  # Redis连接参数             默认:REDIS_PARAMS = {'socket_timeout': 30,'socket_connect_timeout': 30,'retry_on_timeout': True,'encoding': REDIS_ENCODING,})
        # REDIS_PARAMS['redis_cls'] = 'myproject.RedisClient' # 指定连接Redis的Python模块  默认:redis.StrictRedis
        # REDIS_ENCODING = "utf-8"                            # redis编码类型             默认:'utf-8'
    
    b. 去重规则通过redis的集合完成,集合的Key为:
    
        key = defaults.DUPEFILTER_KEY % {'timestamp': int(time.time())}
        默认配置:
            DUPEFILTER_KEY = 'dupefilter:%(timestamp)s'
             
    c. 去重规则中将url转换成唯一标示,然后在redis中检查是否已经在集合中存在
    
        from scrapy.utils import request
        from scrapy.http import Request
        
        req = Request(url='http://www.cnblogs.com/wupeiqi.html')
        result = request.request_fingerprint(req)
        print(result) # 8ea4fd67887449313ccc12e5b6b92510cc53675c 
        
        
        PS: 
            - URL参数位置不同时,计算结果一致;
            - 默认请求头不在计算范围,include_headers可以设置指定请求头
            示例:
                from scrapy.utils import request
                from scrapy.http import Request
                
                req = Request(url='http://www.baidu.com?name=8&id=1',callback=lambda x:print(x),cookies={'k1':'vvvvv'})
                result = request.request_fingerprint(req,include_headers=['cookies',])
                
                print(result)
                
                req = Request(url='http://www.baidu.com?id=1&name=8',callback=lambda x:print(x),cookies={'k1':666})
                
                result = request.request_fingerprint(req,include_headers=['cookies',])
                
                print(result)
        
"""
# Ensure all spiders share same duplicates filter through redis.
# DUPEFILTER_CLASS = "scrapy_redis.dupefilter.RFPDupeFilter"

2. 调度器

"""
调度器,调度器使用PriorityQueue(有序集合)、FifoQueue(列表)、LifoQueue(列表)进行保存请求,并且使用RFPDupeFilter对URL去重
    
    a. 调度器
        SCHEDULER_QUEUE_CLASS = 'scrapy_redis.queue.PriorityQueue'          # 默认使用优先级队列(默认),其他:PriorityQueue(有序集合),FifoQueue(列表)、LifoQueue(列表)
        SCHEDULER_QUEUE_KEY = '%(spider)s:requests'                         # 调度器中请求存放在redis中的key
        SCHEDULER_SERIALIZER = "scrapy_redis.picklecompat"                  # 对保存到redis中的数据进行序列化,默认使用pickle
        SCHEDULER_PERSIST = True                                            # 是否在关闭时候保留原来的调度器和去重记录,True=保留,False=清空
        SCHEDULER_FLUSH_ON_START = True                                     # 是否在开始之前清空 调度器和去重记录,True=清空,False=不清空
        SCHEDULER_IDLE_BEFORE_CLOSE = 10                                    # 去调度器中获取数据时,如果为空,最多等待时间(最后没数据,未获取到)。
        SCHEDULER_DUPEFILTER_KEY = '%(spider)s:dupefilter'                  # 去重规则,在redis中保存时对应的key
        SCHEDULER_DUPEFILTER_CLASS = 'scrapy_redis.dupefilter.RFPDupeFilter'# 去重规则对应处理的类


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

# Default requests serializer is pickle, but it can be changed to any module
# with loads and dumps functions. Note that pickle is not compatible between
# python versions.
# Caveat: In python 3.x, the serializer must return strings keys and support
# bytes as values. Because of this reason the json or msgpack module will not
# work by default. In python 2.x there is no such issue and you can use
# 'json' or 'msgpack' as serializers.
# SCHEDULER_SERIALIZER = "scrapy_redis.picklecompat"

# 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.PriorityQueue'

# Alternative queues.
# SCHEDULER_QUEUE_CLASS = 'scrapy_redis.queue.FifoQueue'
# SCHEDULER_QUEUE_CLASS = 'scrapy_redis.queue.LifoQueue'

# 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  

3. 数据持久化

2. 定义持久化,爬虫yield Item对象时执行RedisPipeline
    
    a. 将item持久化到redis时,指定key和序列化函数
    
        REDIS_ITEMS_KEY = '%(spider)s:items'
        REDIS_ITEMS_SERIALIZER = 'json.dumps'
    
    b. 使用列表保存item数据

4. 起始URL相关

"""
起始URL相关

    a. 获取起始URL时,去集合中获取还是去列表中获取?True,集合;False,列表
        REDIS_START_URLS_AS_SET = False    # 获取起始URL时,如果为True,则使用self.server.spop;如果为False,则使用self.server.lpop
    b. 编写爬虫时,起始URL从redis的Key中获取
        REDIS_START_URLS_KEY = '%(name)s:start_urls'
        
"""
# If True, it uses redis' ``spop`` operation. This could be useful if you
# want to avoid duplicates in your start urls list. In this cases, urls must
# be added via ``sadd`` command or you will get a type error from redis.
# REDIS_START_URLS_AS_SET = False

# Default start urls key for RedisSpider and RedisCrawlSpider.
# REDIS_START_URLS_KEY = '%(name)s:start_urls'

scrapy-redis示例

# DUPEFILTER_CLASS = "scrapy_redis.dupefilter.RFPDupeFilter"
#
#
# from scrapy_redis.scheduler import Scheduler
# from scrapy_redis.queue import PriorityQueue
# SCHEDULER = "scrapy_redis.scheduler.Scheduler"
# SCHEDULER_QUEUE_CLASS = 'scrapy_redis.queue.PriorityQueue'          # 默认使用优先级队列(默认),其他:PriorityQueue(有序集合),FifoQueue(列表)、LifoQueue(列表)
# SCHEDULER_QUEUE_KEY = '%(spider)s:requests'                         # 调度器中请求存放在redis中的key
# SCHEDULER_SERIALIZER = "scrapy_redis.picklecompat"                  # 对保存到redis中的数据进行序列化,默认使用pickle
# SCHEDULER_PERSIST = True                                            # 是否在关闭时候保留原来的调度器和去重记录,True=保留,False=清空
# SCHEDULER_FLUSH_ON_START = False                                    # 是否在开始之前清空 调度器和去重记录,True=清空,False=不清空
# SCHEDULER_IDLE_BEFORE_CLOSE = 10                                    # 去调度器中获取数据时,如果为空,最多等待时间(最后没数据,未获取到)。
# SCHEDULER_DUPEFILTER_KEY = '%(spider)s:dupefilter'                  # 去重规则,在redis中保存时对应的key
# SCHEDULER_DUPEFILTER_CLASS = 'scrapy_redis.dupefilter.RFPDupeFilter'# 去重规则对应处理的类
#
#
#
# REDIS_HOST = '10.211.55.13'                           # 主机名
# REDIS_PORT = 6379                                     # 端口
# # REDIS_URL = 'redis://user:pass@hostname:9001'       # 连接URL(优先于以上配置)
# # REDIS_PARAMS  = {}                                  # Redis连接参数             默认:REDIS_PARAMS = {'socket_timeout': 30,'socket_connect_timeout': 30,'retry_on_timeout': True,'encoding': REDIS_ENCODING,})
# # REDIS_PARAMS['redis_cls'] = 'myproject.RedisClient' # 指定连接Redis的Python模块  默认:redis.StrictRedis
# REDIS_ENCODING = "utf-8"                              # redis编码类型             默认:'utf-8'
配置文件
import scrapy


class ChoutiSpider(scrapy.Spider):
    name = "chouti"
    allowed_domains = ["chouti.com"]
    start_urls = (
        'http://www.chouti.com/',
    )

    def parse(self, response):
        for i in range(0,10):
            yield
爬虫文件

 

 
 
 
posted @ 2017-09-05 19:24  Michael--chen  阅读(274)  评论(0编辑  收藏  举报