我写的UrlManager代码如下：

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 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