說集合是空的，不曉得為啥子

class?UrlManager(object):
????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?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

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