docs: def has_document(self, doc_url):
          """ Check if the content of the given document is present
          in the cache
  
          If the max_age attribute of this Cache is set to a nonzero value,
          entries older than the value of max_age in seconds will be ignored
  
          :type doc_url: String or Document
          :param doc_url: the URL of the document, or a Document object
  
          :rtype: Boolean
          :returns: True if the data is present, False otherwise
  
  
          """
          c = self.conn.cursor()
          c.execute("SELECT * FROM documents WHERE url=?", (str(doc_url),))
          row = c.fetchone()
          c.close()
          return self.__exists_row_not_too_old(row)