demos/demo_nodes_py

• What Is This?
• Build
• Run
• • Basic Listener & Talker
  • Server & Client
  • • Server
    • Client [Synchronous]
    • Client [Asynchronous]
  • QoS Listener & Talker
  • Set Parameters Callback
  • Asynchronous Parameter Client
  • Serialized Subscriber
• Verify
• • Basic Listener & Talker
  • Basic Server & Client
  • • Server
    • Client [Synchronous]
    • Client [Asynchronous]
  • QoS Listener & Talker
  • Set Parameters Callback
  • • [Before]
    • [Change]
    • [After]
  • Asynchronous Parameter Client
  • Serialized Subscriber
• References

What Is This?

This package contains the following ROS 2 nodes:

1. listener
2. talker
3. add_two_ints_client
4. add_two_ints_server
5. set_parameters_callback
6. add_two_ints_client_async
7. listener_qos
8. talker_qos
9. listerner_serialized
10. async_param_client

Build

Run this command to build the package:

colcon build --packages-select demo_nodes_py

Run

Basic Listener & Talker

This runs talker and listener ROS 2 nodes which exchange the following string with incremeting integer:

Hello World: <count_>

# Open new terminal
ros2 run demo_nodes_py talker

# Open new terminal
ros2 run demo_nodes_py listener

Server & Client

This runs add_two_ints_client and add_two_ints_server ROS 2 client and server where the server processes two integers sent from the client and publishes its sum to the client to be printed out.

Server

# Open new terminal
ros2 run demo_nodes_py add_two_ints_server

Client [Synchronous]

# Open new terminal
ros2 run demo_nodes_py add_two_ints_client

Client [Asynchronous]

# Open new terminal
ros2 run demo_nodes_py add_two_ints_client_async

QoS Listener & Talker

Similar to previous, this runs talker_qos and listener_qos ROS 2 nodes which exchange messages using the Quality of Service (QoS) best effort policy.

# Open new terminal
ros2 run demo_nodes_py talker_qos

# Open new terminal
ros2 run demo_nodes_py listener_qos

Set Parameters Callback

This runs set_parameters_callback ROS 2 node which triggers a callback when ROS 2 double parameter param1 is set. The callback then sets ROS 2 double parameter param2 to a fixed 4.0:

# Open new terminal
ros2 run demo_nodes_py set_parameters_callback

Asynchronous Parameter Client

This runs async_param_client ROS 2 node which demonstrates how to set, list, get, load and delete parameters from the parameter blackboard in an asynchronous manner:

# Open new terminal
ros2 run demo_nodes_cpp parameter_blackboard

For more details on parameter_blackboard, please refer to demo_nodes_cpp README.md.

# Open new terminal
ros2 run demo_nodes_py async_param_client

Serialized Subscriber

This runs serialized_subscriber ROS 2 node that subscribes to the ROS 2 topic, /chatter, and deserializes as well as prints out received strings:

# Open new terminal
ros2 run demo_nodes_py listener_serialized

Verify

Basic Listener & Talker

When executed correctly, strings should be printed to the terminal similar to what is shown below:

# In terminal running talker
[INFO] [1674573022.635075580] [talker]: Publishing: "Hello World: 0"
[INFO] [1674573023.593075728] [talker]: Publishing: "Hello World: 1"
[INFO] [1674573024.592438479] [talker]: Publishing: "Hello World: 2"

# In terminal running listener
[INFO] [1674573025.634810166] [listener]: I heard: [Hello World: 0]
[INFO] [1674573026.596392653] [listener]: I heard: [Hello World: 1]
[INFO] [1674573027.596400384] [listener]: I heard: [Hello World: 2]
#...

Basic Server & Client

When executed correctly, strings should be printed to the terminal similar to what is shown below:

Server

# In terminal running add_two_ints_server
[INFO] [1674553268.912391774] [add_two_ints_server]: Incoming request
a: 2 b: 3

Client [Synchronous]

# In terminal running add_two_ints_client
[INFO] [1674553268.912602310] [add_two_ints_client]: Result of add_two_ints: 5

Client [Asynchronous]

# In terminal running add_two_ints_client_async
[INFO] [1674553718.598690033] [add_two_ints_client]: Result of add_two_ints: 5

QoS Listener & Talker

When executed correctly, strings should be printed to the terminal similar to what is shown below:

# In terminal running talker_qos
[INFO] [1674572630.018298164] [talker_qos]: Best effort talker
[INFO] [1674572631.021168516] [talker_qos]: Publishing: "Hello World: 0"
[INFO] [1674572632.021072723] [talker_qos]: Publishing: "Hello World: 1"
[INFO] [1674572633.021197421] [talker_qos]: Publishing: "Hello World: 2"
#...

# In terminal running listener_qos
[INFO] [1674572639.695289182] [listener_qos]: Best effort listener
[INFO] [1674572640.023684925] [listener_qos]: I heard: [Hello World: 0]
[INFO] [1674572641.023416691] [listener_qos]: I heard: [Hello World: 1]
[INFO] [1674572642.024505343] [listener_qos]: I heard: [Hello World: 2]
#...

Set Parameters Callback

[Before]

Run ros2 param get /set_parameters_callback param1 should print the following to the terminal:

Double value is: 0.0

Run ros2 param get /set_parameters_callback param2 should print the following to the terminal:

Double value is 0.0

[Change]

Run ros2 param set /set_parameters_callback param1 28.0 should print the following to the terminal:

Set parameter successful

[After]

Run ros2 param get /set_parameters_callback param1 should print the following to the terminal:

Double value is: 28.0

Run ros2 param get /set_parameters_callback param2 should print the following to the terminal:

Double value is 4.0

Asynchronous Parameter Client

Running ros2 run demo_nodes_cpp parameter_blackboard should print the output to the terminal similar to what is shown below:

# In terminal running async_param_client
[INFO] [1674574042.977327137] [async_param_client]: Setting parameters:
[INFO] [1674574042.978217825] [async_param_client]:     int_parameter:
[INFO] [1674574042.978474500] [async_param_client]:         successful: True
[INFO] [1674574042.978718655] [async_param_client]:     bool_parameter:
[INFO] [1674574042.978960532] [async_param_client]:         successful: True
[INFO] [1674574042.979200840] [async_param_client]:     string_parameter:
[INFO] [1674574042.979446692] [async_param_client]:         successful: True
[INFO] [1674574042.979687030] [async_param_client]: Listing Parameters:
[INFO] [1674574042.980229123] [async_param_client]:     - bool_parameter
[INFO] [1674574042.980476617] [async_param_client]:     - int_parameter
[INFO] [1674574042.980717248] [async_param_client]:     - string_parameter
[INFO] [1674574042.980956813] [async_param_client]: Getting parameters:
[INFO] [1674574042.981544032] [async_param_client]:     - int_parameter: 10
[INFO] [1674574042.981794832] [async_param_client]:     - bool_parameter: False
[INFO] [1674574042.982038493] [async_param_client]:     - string_parameter: Fee Fi Fo Fum
[INFO] [1674574042.982281892] [async_param_client]: Loading parameters:
[INFO] [1674574042.987160462] [async_param_client]:     other_int_parameter:
[INFO] [1674574042.987431457] [async_param_client]:         successful: True
[INFO] [1674574042.987679192] [async_param_client]:         value: 0
[INFO] [1674574042.987920948] [async_param_client]:     int_parameter:
[INFO] [1674574042.988162645] [async_param_client]:         successful: True
[INFO] [1674574042.988402691] [async_param_client]:         value: 12
[INFO] [1674574042.988643394] [async_param_client]:     string_parameter:
[INFO] [1674574042.988884034] [async_param_client]:         successful: True
[INFO] [1674574042.989125729] [async_param_client]:         value: I smell the blood of an Englishman
[INFO] [1674574042.989365771] [async_param_client]:     other_string_parameter:
[INFO] [1674574042.989605537] [async_param_client]:         successful: True
[INFO] [1674574042.989847066] [async_param_client]:         value: One fish, two fish, Red fish, blue fish
[INFO] [1674574042.990086215] [async_param_client]:     bool_parameter:
[INFO] [1674574042.990325361] [async_param_client]:         successful: True
[INFO] [1674574042.990565005] [async_param_client]:         value: False
[INFO] [1674574042.990804701] [async_param_client]: Deleting parameters:
[INFO] [1674574042.991497679] [async_param_client]:     other_int_parameter:
[INFO] [1674574042.991746545] [async_param_client]:         successful: True
[INFO] [1674574042.991986980] [async_param_client]:         reason:
[INFO] [1674574042.992226951] [async_param_client]:     other_string_parameter:
[INFO] [1674574042.992465274] [async_param_client]:         successful: True
[INFO] [1674574042.992703259] [async_param_client]:         reason:
[INFO] [1674574042.992941566] [async_param_client]:     string_parameter:
[INFO] [1674574042.993179508] [async_param_client]:         successful: True
[INFO] [1674574042.993416599] [async_param_client]:         reason:

Serialized Subscriber

Running ros2 run demo_nodes_py talker should print output to the terminal similar to the following:

# In terminal running listener_serialized
[INFO] [1674574499.556053634] [serialized_subscriber]: I heard: "b'\x00\x01\x00\x00\x0f\x00\x00\x00Hello World: 0\x00\x00'"
[INFO] [1674574500.506343148] [serialized_subscriber]: I heard: "b'\x00\x01\x00\x00\x0f\x00\x00\x00Hello World: 1\x00\x00'"
[INFO] [1674574501.508214693] [serialized_subscriber]: I heard: "b'\x00\x01\x00\x00\x0f\x00\x00\x00Hello World: 2\x00\x00'"

References

1. About Quality of Service Settings