#这是我的主代码，

#coding:utf-8
import url_manager,html_downloader,html_parser,html_outputer

class SpiderMain(object):
    def __init__(self):
        # 在构造函数中进行初始化各个对象
        self.urls=url_manager.UrlManager()#url的管理器
        self.downloader=html_downloader.HtmlDownloader()#下载器
        self.parser=html_parser.HtmlParser()#解析器
        self.outputer=html_outputer.HtmlOutputer()#输出器
    # 爬虫的调度程序
    def craw(self,root_url):
        count = 1
        self.urls.add_new_url(root_url)
        while self.urls.has_new_url():
            try:
                new_url = self.urls.get_new_url()
                print('craw %d:%s'%(count,new_url))
                html_cont = self.downloader.download(new_url)
                new_urls,new_data=self.parser.parse(new_url,html_cont)
                self.urls.add_new_urls(new_urls)
                self.outputer.collect_data(new_data)

                if count==1000:
                    break
                count = count+1
            except:
                print('craw failed')

        self.outputer.output_html()    

if __name__=="__main__":
    root_url = "https://baike.baidu.com/item/python/407313"
    obj_spider = SpiderMain()
    obj_spider.craw(root_url)

class UrlManager(object):
    """docstring for UrlManager"""
    def __init__ (self):
        self.new_urls = set()
        self.old_urls = set()

    def add_new_url(self, url):
        if url is None:
            return
        if url not in self.new_urls and url not in self.old_urls:
            self.new_urls.add(url)

    def add_new_urls(self, urls):
        if urls is None or len(urls)==0:
            return
        for url in urls:
            self.add_new_url(url)

    def has_new_url(self):
        return len(self.new_urls) != 0

    def get_new_url(self):
        new_url = self.new_urls.pop()
        self.old_urls.add(new_url)
        return new_url

这是url_manager.py的代码，为什么先显示没有UrlManager的属性呢？很迷惑，找了一天的bug了都没找到，