Groups

group() organizes assets, tasks and sensors in the UI and CLI. It never adds a step, dependency, execution boundary or cache key. A group’s output identifies an existing node; it does not hide other dependencies crossing the group.

from barca import asset, task, group

@asset
def rows():
    return [1, 2, 3]

@asset(inputs={"data": rows})
def model(data):
    return {"count": len(data)}

@task(inputs={"result": model})
def validate_model(result):
    assert result["count"] == 3

training_data = group("Training data", members=[rows], output=rows)
training = group(
    "Training",
    members=[training_data, model, validate_model],
    output=model,
    description="Preparation, fitting and checks",
)
experiment = group("Experiment", members=[training], output=training)

Declare groups at the top level of the file, after their referenced functions/groups, using a literal name, list or tuple of members, output reference, and optional literal description. Assign a group to a variable to nest it in another group; a bare group(...) statement is registered too, under its name, and can only be a root. Groups can nest to any depth. Each node or group has at most one parent. Duplicate membership, unknown references, cycles and outputs outside the group’s descendants are errors. Nodes may remain ungrouped. Members may reference imported nodes from discovered pipeline files; nested groups are currently referenced by their variable in the same file. Computed membership, loops, conditional declarations, strings as references and starred arguments are not supported. Groups cannot be used as inputs= or execution targets.

barca list pipeline.py --groups          # hierarchy, with members and outputs
barca list pipeline.py --groups --json   # {groups: [{id, name, description, members, output}]}
barca list pipeline.py                   # unchanged flat executable-node listing

Group IDs are group:<file>:<variable> (group:<file>:<name> for a group that is not assigned to a variable), separate from <file>:<function> node IDs. Two groups in a file cannot share an ID. The server exposes the same metadata at GET /groups. The UI collapses roots and opens their contents on double click or Enter, retaining nesting across List/Graph. Health aggregates all descendant nodes: any failed member makes its ancestors red, even when the output is cached successfully. CLI group listings show organization; use barca status to inspect execution health.

In serve mode, group metadata uses the same retained graph as node inspection. Groups that reference excluded definitions are omitted and reported through /health.load_errors; healthy executable nodes and other files remain available. One-shot CLI commands continue to reject invalid group declarations.