def _get_bucket(self, bucket_name):
        '''get a bucket based on a bucket name. If it doesn't exist, create it.

           Parameters
           ==========
           bucket_name: the name of the bucket to get (or create). It should
                        not contain google, and should be all lowercase with -
                        or underscores.
        '''

        # Case 1: The bucket already exists
        try:
            bucket = self._bucket_service.get_bucket(bucket_name)

        # Case 2: The bucket needs to be created
        except google.cloud.exceptions.NotFound:
            bucket = self._bucket_service.create_bucket(bucket_name)

        # Case 3: The bucket name is already taken
        except:
            bot.error('Cannot get or create %s' % bucket_name)
            sys.exit(1)

        return bucket
get a bucket based on a bucket name. If it doesn't exist, create it.

           Parameters
           ==========
           bucket_name: the name of the bucket to get (or create). It should
                        not contain google, and should be all lowercase with -
                        or underscores.