Row compute in Python Plasm

The outer Python class declares a typed DAG. Catalog reads acquire rows; row methods transform the materialized result. @compute declares a bounded rendering node with explicit input dependencies.

See the language definition for the supported interface and the semantic matrix for executable coverage.

Operation	Python interface	Meaning
Catalog selection	eN.query(owner="alice")	Arguments use declared CGS input lanes
Row filtering	rows.where(lambda row: row.score >= 10)	Refine already acquired rows
Projection	rows.select("id", "title")	Retain typed columns
Ordering and bounds	rows.order_by("score", descending=True).take(10)	Order, then bound output
Aggregation	rows.aggregate(total=agg.sum("score"))	One synthetic typed row
Grouping	rows.group_by("owner", count=agg.count())	One row per group
Deduplication	rows.distinct("id")	Explicit duplicate removal
Relation fanout	rows.flat_map(lambda row: row.rN)	Declared relation per receiver
Mutation fanout	rows.flat_map(lambda row: row.mN(...))	Reviewed effect per receiver
Rendering	self.report(rows)	Materialize and invoke a declared @compute method

Symbols and signatures come from the current session. These fragments illustrate operations; a submitted program must contain a complete Program subclass.

A rowset in build is a deferred DAG handle, not a Python list. Finite for loops and single-clause list comprehensions over literal string/integer IDs expand into ordinary DAG nodes in source order, with a combined 256-iteration bound. Dynamic Python loops, comprehension filters and arbitrary calls do not declare reviewed nodes. A singleton field can supply a scalar argument. An unbounded plural field cannot silently become one scalar. take(1) fails on empty singleton use and does not establish that the chosen row is the intended identity.

Rendering accepts Python string literals, including multiline and raw strings. Runtime formatting belongs in a typed @compute method. Value[eN] or Row means per-row rendering; list[Value[eN]] or list[Row] means one collection render. Nested structures, arrays, enum constraints, exact money and reference types remain typed.

Optional fields retain their T | None type in compute: check for None before string methods such as .split(). Import date or datetime before using their constructors or clocks. Temporal fields are date/datetime values, not sliceable strings; compare them directly or call .isoformat() for text. A method's input arguments do not become result fields. For a partial write, use only the result fields listed beside that method; acquire other fields through an available read capability.

Writes execute even when unreturned. Subsequent dependent reads must re-observe changed state. Failure or cancellation does not imply rollback. Bounded iteration declares an explicit max_steps and fails if its stop condition remains false at exhaustion.

The original source syntax survives only as an internal semantic oracle in parity tests. It is not accepted by agent-facing hosts.