Parameters are a means of having persistent, but modifiable variables available to nodes.
They may be used for stuff like device paths when accessing hardware, or robot-specific configuration like maximum motor speed. Anything that isn’t constant enough to be hard-coded into a node, but should be more persistent and flexible than environment variables.
Parameters are intended to be specific to each node, however it is possible to access other nodes’ parameters if you need to.
Parameters must be a supported JSON data type, i.e. any standard data type or JSON-compatible object.
You can also have nested parameters (hierarchical parameters), by using dot-notation. For example, Node 1 in the example above could have parameters:
pet_chicken_count
pet_chicken_names
Or alternatively:
chickens.count
chickens.names
Actually, that’s what Node 2 in the example has already done. Accessing their culinary preference likes can be achieved through:
culinary_preferences.likes
Getting a parameter is easy, and can be done at any point within a node.
py
current_menu = self.get_parameter("current_menu")js
const currentMenu = await this.getParameter("current_menu");Setting a parameter can be done in several ways. The simplest is with a declarative function:
py
self.set_parameter("current_menu", ["Tomato soup", "Pork and apple sauce", "Chocolate trifle"])js
this.setParameter("current_menu", [
"Tomato soup",
"Pork and apple sauce",
"Chocolate trifle",
]);You can also set more than one parameter at once:
py
self.set_parameters(
[
{
"name": "menu2",
"value": ["Houmous platter", "Fried plantain", "Toasted marshmallow cookie"],
},
{
"name": "menu3",
"value": ["Deep fried scorpions", "The sensation of time itself", "Stir-fried regret"],
},
]
)js
this.setParameters([
{
name: "menu2",
value: [
"Houmous platter",
"Fried plantain",
"Toasted marshmallow cookie",
],
},
{
name: "menu3",
value: [
"Deep fried scorpions",
"The sensation of time itself",
"Stir-fried regret",
],
},
]);More often than not, however, it makes more sense to store the parameter values in separate config files. They can be in JSON or YAML format (only JSON for Node.js nodes).
node1:
param1: value1
param2: value2
subparam:
subparam1: value1
subparam2: value2{
"node1": {
"param1": "value1",
"param2": "value2",
"subparam": {
"subparam1": "value1",
"subparam2": "value2"
}
}
}These files can be stored somewhere accessible by the running node, and can be parsed and set automatically with:
py
self.set_parameters_from_file(CONFIG_FILE_PATH)js
this.setParametersFromFile(CONFIG_FILE_PATH);