Attribute Enricher

Rule-based attribute enrichment for any sequence of items.

Overview

vcti-attribute-enricher adds attributes to items in a sequence by matching vcti-lookup rules. Each EnrichRule pairs a condition (when) with attributes to write (set); the enricher walks an iterable, evaluates each rule against each item, and stamps matching items with the rule's attributes.

The package is iterable-generic, not tree-specific: the items can be tree-node payloads (e.g., from vcti-fileloader), dicts, dataclasses, or any object with an attribute-bearing surface. Reading and writing are pluggable via getter / setter callables, with sensible defaults for vcti-fileloader's DataNode-shaped payloads.

The package is the write-side counterpart to vcti-lookup: where Lookup filters a sequence by rules, the enricher mutates the sequence by rules.

Installation

pip install vcti-attribute-enricher

In requirements.txt

vcti-attribute-enricher>=1.0.0

In pyproject.toml dependencies

dependencies = [
    "vcti-attribute-enricher>=1.0.0",
]

Quick Start

from vcti.attribute_enricher import EnrichRule, apply_rules
from vcti.lookup import MISSING, Rule

items = [
    {"name": "stress.h5",     "dtype": "float64", "attributes": {}, "enricher_attributes": {}},
    {"name": "ids.h5",        "dtype": "int64",   "attributes": {}, "enricher_attributes": {}},
    {"name": "config.json",   "dtype": "object",  "attributes": {}, "enricher_attributes": {}},
]

def getter(item, key):
    # Read from the item's "attributes" dict, then the top-level item.
    # Return MISSING (not None) when absent so the rule cleanly no-matches.
    if key in item["attributes"]:
        return item["attributes"][key]
    return item.get(key, MISSING)

apply_rules(
    items,
    rules=[
        EnrichRule(set={"loaded_at": "2026-06-06"}),                            # every item
        EnrichRule(set={"category": "mechanical"},
                   when=(Rule("name", "^=", "stress"),)),                        # name starts with "stress"
        EnrichRule(set={"is_numeric": True},
                   when=(Rule("dtype", "^=", "float"),
                         Rule("dtype", "!=", "object"))),                        # AND across rules
    ],
    getter=getter,
    setter=lambda item, key, value: item["enricher_attributes"].__setitem__(key, value),
)

For payloads with a single mutable attribute dict (the common case):

items = [{"name": "x", "tags": {}}, {"name": "y", "tags": {}}]

apply_rules(
    items,
    rules=[EnrichRule(set={"seen": True})],
    getter=lambda item, key: item.get(key, MISSING),
    setter=lambda item, key, value: item["tags"].__setitem__(key, value),
)

Getters must return vcti.lookup.MISSING for absent attributes, not None. None is a legal value that gets passed to the operator; MISSING short-circuits the rule to "no match".

Enriching tree-node payloads

The package's default getter/setter are tuned for vcti-fileloader's DataNode/LazyDataNode payloads, which carry both a read-only file_attributes mapping (file-native) and a mutable enricher_attributes dict. The merged read view is exposed via .attributes (a ChainMap).

from vcti.attribute_enricher import EnrichRule, apply_rules
from vcti.tree import descendants
from vcti.lookup import Rule

apply_rules(
    descendants(tree, subtree_root, include_self=True),
    rules=[
        EnrichRule(set={"file_path": str(path)}),
        EnrichRule(set={"category": "mechanical"},
                   when=(Rule("name", "^=", "stress"),)),
    ],
)

No getter / setter arguments needed — the defaults read item.attributes (ChainMap) and write to item.enricher_attributes.

How it works

1. Iterate the supplied items.
2. For each item, evaluate every EnrichRule:
   • If when is empty, the rule matches.
   • If when has one or more Rules, every rule must match (AND).
   • A rule matches by reading the relevant attribute through getter and evaluating it via vcti.predicate.evaluate (forwarded through vcti-lookup).
3. On a match, write each key/value in set to the item via setter.

Layering — last write wins. Multiple EnrichRules that match the same item all apply, in the order given. Later rules overwrite earlier ones on collision. This makes it easy to express "set a default for everything, then refine for specific subsets."

Return value. apply_rules returns an EnrichResult with summary counts — handy for logging and for spotting dead rules:

result = apply_rules(items, rules)
print(result.items_visited, result.items_matched, result.writes_applied)
print(result.per_rule_matches)   # match count per rule, in order; 0 = dead rule

The items are mutated in place; the result carries metrics only.

API

Values in set are written by reference — a mutable value shared across matched items is the same object on each. See docs/patterns.md for pitfalls.

Dependencies

• vcti-lookup (>=1.0.0) — Rule, MISSING, default attributes_getter
• vcti-predicate (>=1.0.0) — evaluate() is called directly for rule matching