def scrape(self, url):
        '''
        Execute Web-Scraping.
        The target dom objects are in self.__dom_object_list.

        Args:
            url:    Web site url.

        Returns:
            The result. this is a string.

        @TODO(chimera0): check URLs format.
        '''
        if isinstance(url, str) is False:
            raise TypeError("The type of url must be str.")

        if self.readable_web_pdf is not None and self.readable_web_pdf.is_pdf_url(url) is True:
            web_data = self.readable_web_pdf.url_to_text(url)
        else:
            web_data = ""
            req = urllib.request.Request(url=url)
            with urllib.request.urlopen(req) as f:
                web = f.read().decode('utf-8')
                dom = pq(web)
                [dom(remove_object).remove() for remove_object in self.__remove_object_list]

                for dom_object in self.__dom_object_list:
                    web_data += dom(dom_object).text()

        sleep(1)
        return web_data
Execute Web-Scraping.
        The target dom objects are in self.__dom_object_list.

        Args:
            url:    Web site url.

        Returns:
            The result. this is a string.

        @TODO(chimera0): check URLs format.