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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def lookup_users(self, user_ids=None, screen_names=None, include_entities=None, tweet_mode=None):
 """ Perform bulk look up of users from user ID or screen_name """

        post_data = {}
        if include_entities is not None:
            include_entities = 'true' if include_entities else 'false'
            post_data['include_entities'] = include_entities
        if user_ids:
            post_data['user_id'] = list_to_csv(user_ids)
        if screen_names:
            post_data['screen_name'] = list_to_csv(screen_names)
        if tweet_mode:
            post_data['tweet_mode'] = tweet_mode

        return self._lookup_users(post_data=post_data)