StepContext.emit · LSD API

Parameters#

name	type	default	description
`topic`	`str`	—	the event topic — prefer the topic enums, not raw strings
`**data`	`Any`	—	keyword payload delivered to subscribers

Example#

emit is for live, mid-run signals a view or the run report listens for — a progress notice, a "file written" event, a training epoch:

Python

@tool.deliver
def export(t: Table, ctx: StepContext) -> None:
    path = write_parquet(t, ctx.output_dir)
    ctx.emit("file/written", path=path, rows=len(t))

Notes#

Routes through the canonical sync-to-async bridge and is best-effort — a bad handler never fails the step.

emit is not how a deliver shows a result. To put a chart, a geometry layer, or a legend in the viewer, a deliver returns a ViewerPayload — the framework then persists it and emits its viewer/... topic for you, and reconstructs it on reopen (which a bare emit does not):

Python

@tool.deliver
def grades_chart(t: Table) -> ChartPayload:
    ys = [r["grade"] for r in t.to_pylist()]
    return ChartPayload(kind="bar", title="Grades",
                        series=[{"name": "grade", "x": list(range(len(ys))), "y": ys}])

Use the topic enums (ViewerEvents, …) rather than hardcoded strings.

Parameters#

Example#

Notes#

See also#