Python爬虫URL管理器去重机制详解

'''
UrlManager
class UrlManager(object):
  def __init__(self):
    #初始化的时候就生成两个url仓库
    self.new_urls = set()
    self.old_urls = set()
  #判断新url仓库中是否还有没有爬取的url
  def has_new_url(self):
    return len(self.new_urls)
  #从new_url仓库获取一个新的url
  def get_new_url(self):
    return self.new_urls.pop()
  def add_new_url(self, url):  #这个函数后来用不到了……
    '''
    将一条url添加到new_urls仓库中
    parm url: str
    return:
    if url is None:
      return
    #只需要判断old_urls中没有该链接即可，new_urls在添加的时候会自动去重
    if url not in self.old_urls:
      self.new_urls.add(url)
  def add_new_urls(self, urls):
    将多条url添加到new_urls仓库中
    parm url: 可迭代对象
    print "start add_new_urls"
    if urls is None or len(urls) == 0:
    for url in urls:
      self.add_new_url(url)
  def add_old_url(self, url):
    self.old_urls.add(url)
    print "add old url succefully"
  #获取已经爬取过的url的数目
  def old_url_size(self):
    return len(self.old_urls)