code: def create(self, dbsecgroup_id, source_cidr, port=3306):
          
          body = {
                  "security_group_rule": {
                      "security_group_id": dbsecgroup_id,
                      "cidr": source_cidr,
                      "from_port": port,
                      "to_port": port,
                      }
                  }
          return self._create("/security-group-rules", body,
                  "security_group_rule")
docs: Creates a security group rule.
  
          :param str dbsecgroup_id:  The ID of the security group in which this
              rule should be created.
          :param str source_cidr:  The source IP address range from which access
              should be allowed.
          :param int port:  The port number used by db clients to connect to the
              db server.  This would have been specified at db instance creation
              time.
  
          :rtype:  :class:`DBSecurityGroupRule`.