How to use the textract.exceptions.ShellError function in textract

document_id = document_data['id']
            response = requests.get(url)
            # Sometimes, Metro Legistar has a URL that retuns a bad status code (e.g., 404 from http://metro.legistar1.com/metro/attachments/95d5007e-720b-4cdd-9494-c800392b9265.pdf). 
            # Skip these documents.
            if response.status_code != 200:
                logger.error('Document URL {} returns {} - Could not get attachment text!'.format(url, response.status_code))
                continue

            extension = os.path.splitext(url)[1]

            with tempfile.NamedTemporaryFile(suffix=extension) as tfp:
                tfp.write(response.content)

                try:
                    plain_text = textract.process(tfp.name)
                except textract.exceptions.ShellError as e:
                    logger.error('{} - Could not convert Document ID {}!'.format(e, document_id))
                    continue

                logger.info('Document ID {} - conversion complete'.format(document_id))

            yield {'plain_text': plain_text.decode('utf-8'), 'id': document_id}

def convert(self):
        """Converte o PDF baixado anteriormente.

        Faz download de um arquivo PDF, executa o 'parser' do BeautifulSoup
        e transforma o mesmo em uma 'string' utilizando o textract:
        http://textract.readthedocs.io/en/stable/
        """

        import textract
        source_file = self.download()
        try:
            source_binary = textract.process(self.filename, encoding='utf_8',
                                             method='pdftotext', layout=True)
            soup = BeautifulSoup(source_binary, "html.parser")
            text_string = soup.prettify(formatter=None)
        except textract.exceptions.ShellError:
            # TODO: implementar uma maneira de lidar com arquivos nao PDF.
            print('Not a pdf')
            raise NameError('The file is not a .pdf')

        # Apaga o arquivo baixado caso não esteja explícito para salvar
        if not self.save:
            os.remove(self.filename)
        return text_string