demo_nodes_py
Python nodes which were previously in the ros2/examples repository but are now just used for demo purposes.
README
What Is This?
This package contains the following ROS 2 nodes:
listenertalkeradd_two_ints_clientadd_two_ints_serverset_parameters_callbackadd_two_ints_client_asynclistener_qostalker_qoslisterner_serializedasync_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'"