试想一下，前面做的实验和例子都只有一个spider。然而，现实的开发的爬虫肯定不止一个。既然这样，那么就会有如下几个问题：1、在同一个项目中怎么创建多个爬虫的呢？2、多个爬虫的时候是怎么将他们运行起来呢？
说明：本文章是基于前面几篇文章和实验的基础上完成的。如果您错过了，或者有疑惑的地方可以在此查看：
scrapy爬虫成长日记之创建工程-抽取数据-保存为json格式的数据
一、创建spider
1、创建多个spider，scrapy genspider spidername domain
scrapy genspider CnblogsHomeSpider cnblogs.com
通过上述命令创建了一个spider name为CnblogsHomeSpider的爬虫，start_urls为http://www.cnblogs.com/的爬虫
2、查看项目下有几个爬虫scrapy list
[root@bogon cnblogs]# scrapy listCnblogsHomeSpider
CnblogsSpider
由此可以知道我的项目下有两个spider，一个名称叫CnblogsHomeSpider，另一个叫CnblogsSpider。
更多关于scrapy命令可参考：http://doc.scrapy.org/en/latest/topics/commands.html
二、让几个spider同时运行起来
现在我们的项目有两个spider，那么现在我们怎样才能让两个spider同时运行起来呢？你可能会说写个shell脚本一个个调用，也可能会说写个python脚本一个个运行等。然而我在stackoverflow.com上看到。的确也有不上前辈是这么实现。然而官方文档是这么介绍的。
1、Run Scrapy from a script
import scrapyfrom scrapy.crawler import CrawlerProcessclass MySpider(scrapy.Spider):
# Your spider definition …
process = CrawlerProcess({
‘USER_AGENT’: ‘Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1)’})
process.crawl(MySpider)
process.start() # the script will block here until the crawling is finished
这里主要通过scrapy.crawler.CrawlerProcess来实现在脚本里运行一个spider。更多的例子可以在此查看：https://github.com/scrapinghub/testspiders
2、Running multiple spiders in the same process
通过CrawlerProcess
import scrapyfrom scrapy.crawler import CrawlerProcessclass MySpider1(scrapy.Spider):
# Your first spider definition …class MySpider2(scrapy.Spider):
# Your second spider definition …
process = CrawlerProcess()
process.crawl(MySpider1)
process.crawl(MySpider2)
process.start() # the script will block here until all crawling jobs are finished
通过CrawlerRunner
import scrapyfrom twisted.internet import reactorfrom scrapy.crawler import CrawlerRunnerfrom scrapy.utils.log import configure_loggingclass MySpider1(scrapy.Spider):
# Your first spider definition …class MySpider2(scrapy.Spider):
# Your second spider definition …
configure_logging()
runner = CrawlerRunner()
runner.crawl(MySpider1)
runner.crawl(MySpider2)
d = runner.join()
d.addBoth(lambda _: reactor.stop())
reactor.run() # the script will block here until all crawling jobs are finished
通过CrawlerRunner和链接(chaining) deferred来线性运行
from twisted.internet import reactor, deferfrom scrapy.crawler import CrawlerRunnerfrom scrapy.utils.log import configure_loggingclass MySpider1(scrapy.Spider):
# Your first spider definition …class MySpider2(scrapy.Spider):
# Your second spider definition …
configure_logging()
runner = CrawlerRunner()
@defer.inlineCallbacksdef crawl():
yield runner.crawl(MySpider1)
yield runner.crawl(MySpider2)
reactor.stop()
crawl()
reactor.run() # the script will block here until the last crawl call is finished
这是官方文档提供的几种在script里面运行spider的方法。
三、通过自定义scrapy命令的方式来运行
1、创建commands目录
mkdir commands
注意：commands和spiders目录是同级的
2、在commands下面添加一个文件crawlall.py
这里主要通过修改scrapy的crawl命令来完成同时执行spider的效果。crawl的源码可以在此查看：https://github.com/scrapy/scrapy/blob/master/scrapy/commands/crawl.py
from scrapy.commands import ScrapyCommand from scrapy.crawler import CrawlerRunnerfrom scrapy.utils.conf import arglist_to_dictclass Command(ScrapyCommand):
requires_project = True
def syntax(self):
return ‘[options]’
def short_desc(self):
return ‘Runs all of the spiders’
def add_options(self, parser):
ScrapyCommand.add_options(self, parser)
parser.add_option(“-a”, dest=”spargs”, action=”append”, default=[], metavar=”NAME=VALUE”,
help=”set spider argument (may be repeated)”)
parser.add_option(“-o”, “–output”, metavar=”FILE”,
help=”dump scraped items into FILE (use – for stdout)”)
parser.add_option(“-t”, “–output-format”, metavar=”FORMAT”,
help=”format to use for dumping items with -o”)
def process_options(self, args, opts):
ScrapyCommand.process_options(self, args, opts)
try:
opts.spargs = arglist_to_dict(opts.spargs)
except ValueError:
raise UsageError(“Invalid -a value, use -a NAME=VALUE”, print_help=False)
def run(self, args, opts):
#settings = get_project_settings() spider_loader = self.crawler_process.spider_loader
for spidername in args or spider_loader.list():
print “*********cralall spidername************” + spidername
self.crawler_process.crawl(spidername, **opts.spargs)
self.crawler_process.start()
这里主要是用了self.crawler_process.spider_loader.list()方法获取项目下所有的spider，然后利用self.crawler_process.crawl运行spider
3、commands命令下添加__init__.py文件
touch __init__.py
注意：这一步一定不能省略。我就是因为这个问题折腾了一天。囧。。。就怪自己半路出家的吧。
如果省略了会报这样一个异常
Traceback (most recent call last):
File “/usr/local/bin/scrapy”, line 9, in
load_entry_point(‘Scrapy==1.0.0rc2’, ‘console_scripts’, ‘scrapy’)()
File “/usr/local/lib/python2.7/site-packages/Scrapy-1.0.0rc2-py2.7.egg/scrapy/cmdline.py”, line 122, in execute
cmds = _get_commands_dict(settings, inproject)
File “/usr/local/lib/python2.7/site-packages/Scrapy-1.0.0rc2-py2.7.egg/scrapy/cmdline.py”, line 50, in _get_commands_dict
cmds.update(_get_commands_from_module(cmds_module, inproject))
File “/usr/local/lib/python2.7/site-packages/Scrapy-1.0.0rc2-py2.7.egg/scrapy/cmdline.py”, line 29, in _get_commands_from_module
for cmd in _iter_command_classes(module):
File “/usr/local/lib/python2.7/site-packages/Scrapy-1.0.0rc2-py2.7.egg/scrapy/cmdline.py”, line 20, in _iter_command_classes
for module in walk_modules(module_name):
File “/usr/local/lib/python2.7/site-packages/Scrapy-1.0.0rc2-py2.7.egg/scrapy/utils/misc.py”, line 63, in walk_modules
mod = import_module(path)
File “/usr/local/lib/python2.7/importlib/__init__.py”, line 37, in import_module
__import__(name)
ImportError: No module named commands
一开始怎么找都找不到原因在哪。耗了我一整天，后来到http://stackoverflow.com/上得到了网友的帮助。再次感谢万能的互联网，要是没有那道墙该是多么的美好呀！扯远了，继续回来。
4、settings.py目录下创建setup.py（这一步去掉也没影响，不知道官网帮助文档这么写有什么具体的意义。）
from setuptools import setup, find_packages
setup(name=’scrapy-mymodule’,
entry_points={
‘scrapy.commands’: [
‘crawlall=cnblogs.commands:crawlall’,
],
},
)
这个文件的含义是定义了一个crawlall命令，cnblogs.commands为命令文件目录，crawlall为命令名。
5. 在settings.py中添加配置：
COMMANDS_MODULE = ‘cnblogs.commands’
6. 运行命令scrapy crawlall
