ros2 run demo_nodes_py talker
ros2 run demo_nodes_py listener

ros2 topic list
ros2 topic echo /chatter

ros2 run turtlesim turtlesim_node
ros2 run turtlesim turtle_teleop_key

ros2 topic list
ros2 topic echo /turtle1/cmd_vel
ros2 topic info /turtle1/cmd_vel
ros2 interface show geometry_msgs/msg/Twist

class DrawCircleNode(Node):
    def __init__(self):
        super().__init__("draw_circle")
        self.cmd_vel_pub = self.create_publisher(Twist, "/turtle1/cmd_vel", 10)
        self.timer = self.create_timer(0.5, self.send_velocity_command)

    def send_velocity_command(self):
        msg = Twist()
        msg.linear.x = 2.0
        msg.angular.z = 1.0
        self.cmd_vel_pub.publish(msg)

class PoseSubscriberNode(Node):
    def __init__(self):
        super().__init__("pose_subscriber")
        self.subscription = self.create_subscription(
            Pose, "/turtle1/pose", self.pose_callback, 10)

    def pose_callback(self, msg):
        self.get_logger().info(
            f"x: {msg.x}, y: {msg.y}, theta: {msg.theta}")

colcon build --symlink-install
source install/setup.bash

ros2 run my_first_py_pkg draw_circle
ros2 run my_first_py_pkg pose_subscriber   # separate terminal

rqt_graph
ros2 topic list
ros2 topic echo /topic