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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 register_user(self, username, groups=None, policies=None, mount_point=DEFAULT_MOUNT_POINT):
 """Register a new user and maps a set of policies to it. Supported methods: POST: /auth/{mount_point}/users/{username}. Produces: 204 (empty body) :param username: Name of the user. :type username: str | unicode :param groups: List or comma-separated string of groups associated with the user. :type groups: list :param policies: List or comma-separated string of policies associated with the user. :type policies: list :param mount_point: The "path" the method/backend was mounted on. :type mount_point: str | unicode :return: The response of the request. :rtype: requests.Response """

        params = {
            'username': username,
            'groups': groups,
            'policies': policies,
        }
        api_path = '/v1/auth/{mount_point}/users/{username}'.format(
            mount_point=mount_point,
            username=username,
        )
        return self._adapter.post(
            url=api_path,
            json=params,
        )