docs: def db_import(self, urls=None, force_download=False):
          """Updates the CTD database
          
          1. downloads all files from CTD
          2. drops all tables in database
          3. creates all tables in database
          4. import all data from CTD files
          
          :param iter[str] urls: An iterable of URL strings
          :param bool force_download: force method to download
          """
          if not urls:
              urls = [
                  defaults.url_base + table_conf.tables[model]['file_name']
                  for model in table_conf.tables
              ]
  
          log.info('Update CTD database from %s', urls)
  
          self.drop_all()
          self.download_urls(urls=urls, force_download=force_download)
          self.create_all()
          self.import_tables()
          self.session.close()