Example:

Build the node

 mkdir colcon_ws
 mkdir colcon_ws/src
 cd colcon_ws/src
 git clone https://github.com/picknikrobotics/generate_parameter_library.git
 cd ..
 colcon build

Run the Python node

source install/setup.bash
ros2 run generate_parameter_module_example test_node --ros-args --params-file src/generate_parameter_library/example_python/config/implementation.yaml

You should see an output like this: [INFO] [1656018676.015816509] [admittance_controller]: Initial control frame parameter is: 'ee_link'

ROS 2 CLI

Run the following:

ros2 param list

You should see:

/admittance_controller:
  admittance.damping_ratio
  admittance.mass
  admittance.selected_axes
  admittance.stiffness
  chainable_command_interfaces
  command_interfaces
  control.frame.external
  control.frame.id
  enable_parameter_update_without_reactivation
  fixed_array
  fixed_string
  fixed_string_no_default
  fixed_world_frame.frame.external
  fixed_world_frame.frame.id
  ft_sensor.filter_coefficient
  ft_sensor.frame.external
  ft_sensor.frame.id
  ft_sensor.name
  gravity_compensation.CoG.force
  gravity_compensation.CoG.pos
  gravity_compensation.frame.external
  gravity_compensation.frame.id
  interpolation_mode
  joints
  kinematics.alpha
  kinematics.base
  kinematics.group_name
  kinematics.plugin_name
  kinematics.plugin_package
  kinematics.tip
  one_number
  pid.elbow_joint.d
  pid.elbow_joint.i
  pid.elbow_joint.p
  pid.rate
  pid.shoulder_lift_joint.d
  pid.shoulder_lift_joint.i
  pid.shoulder_lift_joint.p
  pid.shoulder_pan_joint.d
  pid.shoulder_pan_joint.i
  pid.shoulder_pan_joint.p
  pid.wrist_1_joint.d
  pid.wrist_1_joint.i
  pid.wrist_1_joint.p
  pid.wrist_2_joint.d
  pid.wrist_2_joint.i
  pid.wrist_2_joint.p
  pid.wrist_3_joint.d
  pid.wrist_3_joint.i
  pid.wrist_3_joint.p
  qos_overrides./parameter_events.publisher.depth
  qos_overrides./parameter_events.publisher.durability
  qos_overrides./parameter_events.publisher.history
  qos_overrides./parameter_events.publisher.reliability
  scientific_notation_num
  state_interfaces
  three_numbers
  three_numbers_of_five
  use_feedforward_commanded_input
  use_sim_time
  

All parameter are automatically declared and callbacks are setup by default. You can set a parameter by typing:

ros2 param set /admittance_controller control.frame.id new_frame

You should see:

[INFO] [1656019001.515820371] [admittance_controller]: New control frame parameter is: 'new_frame'

Congratulations, you updated the parameter!

If you try to set a parameter that is read only, you will get an error. Running the following

ros2 param set /admittance_controller command_interfaces ["velocity"]

will result in the error

Setting parameter failed: Trying to set a read-only parameter: command_interfaces.

Running the following

ros2 param describe /admittance_controller admittance.damping_ratio

will show a parameter’s description

 Parameter name: admittance.damping_ratio
  Type: double array
  Description: specifies damping ratio values for x, y, z, rx, ry, and rz used in the admittance calculation. The values are calculated as damping can be used instead: zeta = D / (2 * sqrt( M * S ))
  Constraints:
    Min value: 0.1
    Max value: 10.0

If you try to set a value out of the specified bounds,

ros2 param set /admittance_controller admittance.damping_ratio [-10.0,-10.0,-10.0,-10.0,-10.0,-10.0]

you will get the error

Setting parameter failed: Value array('d', [-10.0, -10.0, -10.0, -10.0, -10.0, -10.0]) in parameter 'admittance.damping_ratio' must be within bounds [0.1, 10.0]

If you try to set a vector parameter with the wrong length,

ros2 param set /admittance_controller admittance.damping_ratio [1.0,1.0,1.0]

you will get the error

Setting parameter failed: Length of parameter 'admittance.damping_ratio' is '3' but must be equal to 6

If you try to load a yaml file with missing required parameters

ros2 run generate_parameter_module_example test_node --ros-args --params-file src/generate_parameter_library/example_python/config/missing_required.yaml

you will get the error

Traceback (most recent call last):
[...]
rclpy.exceptions.ParameterUninitializedException: The parameter 'fixed_string_no_default' is not initialized
[ros2run]: Process exited with failure 1

Changelog for package generate_parameter_module_example

0.3.9 (2024-10-27)

• Add "additional_constraints" support (#221)
• Drop yaml brackets for consistency and readability (#203)
• Contributors: David Revay, Tim Clephas

0.3.8 (2024-03-27)

• Restore functionality for mapped params with no struct name ([#185 <https://github.com/PickNikRobotics/generate_parameter_library/issues/185>_]{.title-ref})
• Fix newline issue (#176)
  • fix new line rendering for Python
• Support nested mapped parameters (#166)
• Contributors: Paul Gesel, Sebastian Castro

0.3.7 (2024-01-12)

• Fix rolling CI (#162)
• Split example/README.md into C++ and Python version; updated content (#138)
• Contributors: Paul Gesel, chriseichmann

0.3.6 (2023-07-31)

• Prevent module import when running [setup.py clean]{.title-ref} (#137)
• Contributors: Paul Gesel

0.3.5 (2023-07-28)

• add dependency to python example package (#136)
• Contributors: Paul Gesel

0.3.4 (2023-07-24)

• Fix Python install (#122)
• Add Python support for generate_parameter_library (#110) Co-authored-by: Tyler Weaver <<tyler@picknik.ai>>
• Contributors: Paul Gesel