code: def get_document(self, doc_url):
          
          c = self.conn.cursor()
          c.execute("SELECT * FROM documents WHERE url=?", (str(doc_url),))
          row = c.fetchone()
          c.close()
          if row is None:
              raise ValueError("Item not present in cache")
          file_path = row[1]
          try:
              with open(file_path, 'rb') as f:
                  return f.read()
          except IOError as e:
              raise IOError("Error reading file " + file_path +
                            " to retrieve document " + doc_url +
                            ": " + e.message)
docs: Retrieve the content for the given document from the cache.
  
          :type doc_url: String or Document
          :param doc_url: the URL of the document, or a Document object
  
          :rtype: String
          :returns: the document data
  
          :raises: ValueError if the item is not in the cache