#! /usr/bin/env python3
# coding=utf-8

class Urls():
	def __init__(self):
		self.newurls = set()
		self.oldurls = set()

	def add_one_url(self, root_url):
		if root_url is None:
			return
		if root_url not in self.newurls and root_url not in self.oldurls:
			self.newurls.add(root_url)

	def has_one_url(self):
		return len(self.newurls) != 0

	def get_one_url(self):
		one_url =self.newurls.pop()
		self.oldurls.add(one_url)
		return one_url

	def delete_url(self):
		self.newurls.clear()
		self.oldurls.clear()