msg数据类型 C++数据类型 python数据类型
    bool uint8_t bool
    int8 int8_t int
    int16 int16_t int
    int32 int32_t int
    int64 int64_t int，long
    uint8 uint8_t int
    uint16 uint16_t int
    uint32 uint32_t int
    uint64 uint64_t int，long
    float32 float float
    float64 float float
    string std:string str，bytes
    time ros:Time rospy.Time
    duration ros::Duration rospy.Duration