class sftp:
    def __init__(self):
        self.response = HttpResponse()
        self.cnopts = pysftp.CnOpts()
        self.cnopts.hostkeys = None
    def dl(self):
        with pysftp.Connection('host.exmaple.com', username='user1', password='test_password',
                               cnopts=self.cnopts) as sftp:
            sftp.getfo(
                '/var/lib/stuff/file.mp3',
                self.response)
            self.response['Content-Type'] = 'audio/mp3'
        return self.response

return sftp().download()