Scrapy源码剖析之自定义low版框架

Posted 2022-09-15 jintian

isinstance(result,types.GeneratorType)　　判断是否生成器

队列为空会等，block=False　　不等会报错

reactor.callLater(0,self.next_request)

from twisted.internet import reactor   # 事件循环（终止条件，所有的socket都已经移除）
from twisted.web.client import getPage # socket对象（如果下载完成，自动从时间循环中移除...）
from twisted.internet import defer     # defer.Deferred 特殊的socket对象 （不会发请求，手动移除）

class Request(object):

    def __init__(self,url,callback):
        self.url = url
        self.callback = callback
class HttpResponse(object):

    def __init__(self,content,request):
        self.content = content
        self.request = request
        self.url = request.url
        self.text = str(content,encoding=‘utf-8‘)


class ChoutiSpider(object):
    name = ‘chouti‘

    def start_requests(self):
        start_url = [‘http://www.baidu.com‘,‘http://www.bing.com‘,]
        for url in start_url:
            yield Request(url,self.parse)

    def parse(self,response):
        print(response) #response是下载的页面
        yield Request(‘http://www.cnblogs.com‘,callback=self.parse)

import queue
Q = queue.Queue()

class Engine(object):

    def __init__(self):
        self._close = None
        self.max = 5
        self.crawlling = []

    def get_response_callback(self,content,request):
        self.crawlling.remove(request)
        rep = HttpResponse(content,request)
        result = request.callback(rep)
        import types
        if isinstance(result,types.GeneratorType):
            for req in result:
                Q.put(req)



    def _next_request(self):
        """
        去取request对象，并发送请求
        最大并发数限制
        :return:
        """
        print(self.crawlling,Q.qsize())
        if Q.qsize() == 0 and len(self.crawlling) == 0:
            self._close.callback(None)
            return

        if len(self.crawlling) >= self.max:
            return
         while len(self.crawlling) < self.max:
            try:
                req = Q.get(block=False)
                self.crawlling.append(req)
                d = getPage(req.url.encode(‘utf-8‘))
                # 页面下载完成，get_response_callback，调用用户spider中定义的parse方法，并且将新请求添加到调度器
                d.addCallback(self.get_response_callback,req)
                # 未达到最大并发数，可以再去调度器中获取Request
                d.addCallback(lambda _:reactor.callLater(0, self._next_request))
            except Exception as e:
                print(e)
                return

    @defer.inlineCallbacks
    def crawl(self,spider):
        # 将初始Request对象添加到调度器
        start_requests = iter(spider.start_requests())
        while True:
            try:
                request = next(start_requests)
                Q.put(request)
            except StopIteration as e:
                break

        # 去调度器中取request，并发送请求
        # self._next_request()
        reactor.callLater(0, self._next_request)

        self._close = defer.Deferred()
        yield self._close

spider = ChoutiSpider()


_active = set()
engine = Engine()
d = engine.crawl(spider)
_active.add(d)

dd = defer.DeferredList(_active)
dd.addBoth(lambda a:reactor.stop())

reactor.run()

自定义Scrapy框架.py