爬虫：（在这里不用配置start_url，直接可以取redis里面取start_url，可以多个）
from scrapy_redis.spiders import RedisSpider
# class ChoutiSpider(scrapy.Spider):
class ChoutiSpider(RedisSpider):
name = 'baidu'##在这里设置了这个name，那么在redispider里面就可以按照这个key来找到里面对应的值（开始url，可能多个），
#key的格式是:self.redis_key = self.redis_key % {'name': self.name}
allowed_domains = ['baidu.com']
def parse(self, response):
print('执行操作')
print(response)
在settings里面的配置：
#true的话，就是集合，false的话，就为列表
REDIS_START_URLS_AS_SET=False#默认是false，列表的格式取数据出来
# REDIS_START_URLS_KEY = '%(name)s:start_urls'#不设置默认是这个,这个是存入redis里面的key，可以根据这来取value，例如:baidu:start_urls
如果是列表的话，取数据是lpop(key)，key就是下面的这个
如果是集合的话，集合取数据是spop(key)，例如：spop('baidu:start_urls')>>后面就是对应的全部的开始url（可以多个）
redis存入开始url:
在了一个.py文件里面存入开始url
列表：
import redis
conn=redis.Redis(host='127.0.0.1',port=6379)
conn.lpush('baidu:start_urls','http://www.baidu.com')
如果是settings里面：
REDIS_START_URLS_AS_SET=False的话，就是列表的形式，存入就是lpush或者是rpush等操作
如果是true的话，那么存入就是集合的形式，sadd等操作
集合：
import redis
conn=redis.Redis(host='127.0.0.1',port=6379)
conn.sadd('baidu:start_urls','http://www.baidu.com')##按照这个格式来存数据的
print(conn.smembers('baidu:start_urls'))
scrapy_redis里面的spider源码分析：
class RedisMixin(object):
"""Mixin class to implement reading urls from a redis queue."""
redis_key = None
redis_batch_size = None
redis_encoding = None
# Redis client placeholder.
server = None
def start_requests(self):
"""Returns a batch of start requests from redis."""
return self.next_requests()
def setup_redis(self, crawler=None):
"""Setup redis connection and idle signal.
This should be called after the spider has set its crawler object.
"""
if self.server is not None:
return
if crawler is None:
# We allow optional crawler argument to keep backwards
# compatibility.
# XXX: Raise a deprecation warning.
crawler = getattr(self, 'crawler', None)
if crawler is None:
raise ValueError("crawler is required")
settings = crawler.settings
#####去配置文件里面那这个其始url,START_URLS_KEY = '%(name)s:start_urls',如果没有配置文件的话，就读取后面部分
if self.redis_key is None:
self.redis_key = settings.get(
'REDIS_START_URLS_KEY', defaults.START_URLS_KEY,
)##在这里可以自己设置这个格式，REDIS_START_URLS_KEY在settigs里面设置成自己想要保存的格式，注意：自己就按照这个
，格式进行保存，下面就以这个格式作为键进行查找到相对应的全部的开始url
self.redis_key = self.redis_key % {'name': self.name}####在这里设置这个name的redis查询的key,如果在redis里面有这个key存在的话，就取出里面的值进行查找
'''
所以可以自己在添加开始到这个name里面去，这个key格式是固定的,START_URLS_KEY = '%(name)s:start_urls'''
######写入redis的这个key里面存进去，里面可以放url，多个，然后拿到多个开始的url
if not self.redis_key.strip():
raise ValueError("redis_key must not be empty")
if self.redis_batch_size is None:
# TODO: Deprecate this setting (REDIS_START_URLS_BATCH_SIZE).
self.redis_batch_size = settings.getint(
###取配置文件里面取值，后面是int的类型，转化为int的类型
'REDIS_START_URLS_BATCH_SIZE',
settings.getint('CONCURRENT_REQUESTS'),
)
try:
self.redis_batch_size = int(self.redis_batch_size)
except (TypeError, ValueError):
raise ValueError("redis_batch_size must be an integer")
if self.redis_encoding is None:
self.redis_encoding = settings.get('REDIS_ENCODING', defaults.REDIS_ENCODING)
self.logger.info("Reading start URLs from redis key '%(redis_key)s' "
"(batch size: %(redis_batch_size)s, encoding: %(redis_encoding)s",
self.__dict__)
self.server = connection.from_settings(crawler.settings)
# The idle signal is called when the spider has no requests left,
# that's when we will schedule new requests from redis queue
crawler.signals.connect(self.spider_idle, signal=signals.spider_idle)
def next_requests(self):
"""Returns a request to be scheduled or none."""
use_set = self.settings.getbool('REDIS_START_URLS_AS_SET', defaults.START_URLS_AS_SET)
fetch_one = self.server.spop if use_set else self.server.lpop
##做了判断，如果是REDIS_START_URLS_AS_SET=True得话，那么就为集合
##做了判断，如果是REDIS_START_URLS_AS_SET=False得话，那么就为列表
# XXX: Do we need to use a timeout here?
found = 0
# TODO: Use redis pipeline execution.
####在下面进行寻找，如果存在这个redis_key的话，就执行，有多个就执行多个其实url，
''''
下面是一直循环着，看有没有其实url，在redis里面，这个格式是,REDIS_START_URLS_KEY = '%(name)s:start_urls'>>
当为false的时候，就是以列表的形式查找
conn.lpush('baidu:start_urls','http://www.baidu.com')
当true的时候，就是集合
'''
while found < self.redis_batch_size:
data = fetch_one(self.redis_key)##可能是spop或者是lpop
if not data:
# Queue empty.
break
req = self.make_request_from_data(data)
if req:
yield req
found += 1
else:
self.logger.debug("Request not made from data: %r", data)
if found:
self.logger.debug("Read %s requests from '%s'", found, self.redis_key)
def make_request_from_data(self, data):
"""Returns a Request instance from data coming from Redis.
By default, ``data`` is an encoded URL. You can override this method to
provide your own message decoding.
Parameters
----------
data : bytes
Message from redis.
"""
url = bytes_to_str(data, self.redis_encoding)
return self.make_requests_from_url(url)
def schedule_next_requests(self):
"""Schedules a request if available"""
# TODO: While there is capacity, schedule a batch of redis requests.
for req in self.next_requests():
self.crawler.engine.crawl(req, spider=self)
def spider_idle(self):
"""Schedules a request if available, otherwise waits."""
# XXX: Handle a sentinel to close the spider.
self.schedule_next_requests()
raise DontCloseSpider
