报错NameError: name 'url_manager' is not defined

class SpiderMain(object):

def __init__(self):

self.urls = url_manager.UrlManager()

self.downloader = html_downloader.HtmlDownloader()

self.parser = html_parser.HtmlParser()

self.output = html_outputer.HtmlOutputer()

def craw(self, root_url):

self.urls.add_new_url(root_url)

while self.urls.has_new_url():

new_url = self.urls.get_new_url()

print("第",count, '条: ', new_url)

html_cont = self.downloader.download()

new_urls, new_data = self.parser.parse(new_url, html_cont)

self.urls.add_new_urls(new_urls)

self.output.collect_data(new_data)

if count == 1000:

break

count += 1

self.output.output_html()

root_url="https://baike.baidu.com/item/Python/407313"

obj_spider = SpiderMain()

obj_spider.craw(root_url)