'Get list of all subscriptions to a specific topic.
:type topic: string
:param topic: The ARN of the topic for which you wish to
find subscriptions.
:type next_token: string
:param next_token: Token returned by the previous call to
this method.'

def get_all_subscriptions_by_topic(self, topic, next_token=None):

    params = {'TopicArn': topic}
    if next_token:
        params['NextToken'] = next_token
    return self._make_request('ListSubscriptionsByTopic', params)
