def get_vocab(self, vocab_name, **kwargs):
        """ Returns data stream of an rdf vocabulary

        args:
            vocab_name: the name or uri of the vocab to return
        """
        vocab_dict = self.__get_vocab_dict__(vocab_name, **kwargs)

        filepaths = list(set([os.path.join(self.cache_dir,
                                           vocab_dict['filename']),
                              os.path.join(self.vocab_dir,
                                           vocab_dict['filename'])]))
        for path in filepaths:
            if os.path.exists(path):
                with open(path, 'rb') as f_obj:
                    vocab_dict.update({"name": vocab_name,
                                       "data": f_obj.read(),
                                       "modified": os.path.getmtime(path)})
                return vocab_dict
        download_locs = make_list(vocab_dict.get('download',[]))
        for loc in download_locs:

            loc_web = urllib.request.urlopen(loc)
            # loc_file_date = date_parse(loc_web.info()['Last-Modified'])
            urllib.request.urlretrieve(loc, filepaths[0])
            with open(filepaths[0], 'rb') as f_obj:
                vocab_dict.update({"name": vocab_name,
                                   "data": f_obj.read(),
                                   "modified": os.path.getmtime(filepaths[0])})
                return vocab_dict
Returns data stream of an rdf vocabulary

        args:
            vocab_name: the name or uri of the vocab to return