navrules

Generic, low-latency rule evaluation engine with priority-ordered first-match, declarative conditions, and an optional Rust backend for the CPU-bound hot path.

Extracted from a production rewards system; designed to be shared by any consumer that evaluates "subject + environment vs. N rules": rewards/badges, payrate selection at clock-out, eligibility checks, etc.

• Zero mandatory dependencies — stdlib only; pandas and cel are extras.
• Two-phase rule contract — fits(ctx, env) (sync, cheap pre-filter) and async evaluate(ctx, env) (full evaluation, may do I/O).
• Policies — ALL_MATCH, ANY_MATCH, FIRST_MATCH (priority-ordered, short-circuiting, typed result payload).
• Rust hot path — declarative rule sets compile once into a native matcher (PyO3 + rayon, GIL released); pure-Python fallback is always available (navrules.HAS_RUST tells you which one is active).

Quick start: payrate selection at clock-out

from navrules import ConditionRule, EvalContext, Environment, Policy, RuleSet

ruleset: RuleSet[dict] = RuleSet(
    policy=Policy.FIRST_MATCH,
    default={"payrate": 25.0, "code": "BASE"},
)
ruleset.add_rule({
    "rule_type": "ConditionRule",
    "name": "ot_weekend",
    "priority": 100,
    "conditions": {"env.is_weekend": True, "ctx.worked_hours": {"gt": 8}},
    "result": {"payrate": 33.75, "code": "OT-WKND"},
})
ruleset.add_rule({
    "rule_type": "ConditionRule",
    "name": "night_diff",
    "priority": 90,
    "conditions": {
        "env.day_period": {"in": ["evening", "night"]},
        "ctx.job_code": {"in": ["TECH1", "TECH2"]},
    },
    "result": {"payrate": 29.50, "code": "NIGHT"},
})
ruleset.compile()  # sorts by priority, compiles to Rust when available

# hot path — one call per clock-out, no async, no I/O:
env = Environment.at(clockout_ts, tz=site_tz)
ctx = EvalContext.from_user(employee, worked_hours=9.5, job_code="TECH1")
result = ruleset.evaluate_sync(ctx, env)
payrate = result.value["payrate"]

# end-of-day close, thousands of activities (rayon batch):
results = ruleset.evaluate_batch(contexts, env)

Condition DSL

JSON-friendly dict, one entry per field (entries AND together):

{
    "env.is_weekend": true,
    "ctx.worked_hours": {"gte": 4, "lt": 12},
    "ctx.job_code": {"in": ["TECH1", "TECH2"]},
    "quarter": "Q4"
}

• Scalar value ⇒ eq shorthand. A {op: operand} map applies operators; multiple operators under one field AND together.
• ctx. prefix reads the evaluation context, env. the environment; bare keys resolve ctx first, then env.
• Operators: eq ne gt gte lt lte in not_in contains startswith endswith regex between is_null.
• Missing values match only is_null; bool never coerces to a number; int/float coerce to each other. The Rust backend mirrors these semantics bit-for-bit (enforced by the parity suite).
• Custom operators can be registered on an OperatorRegistry; rule sets using them transparently fall back to the Python matcher.

Rule families

Mixed sets work: await ruleset.evaluate(ctx, env) walks rules in priority order, awaiting I/O rules in their turn.

Environment

Environment derives ~35 temporal fields from a single timestamp (is_weekend, quarter, day_period, week_position, is_pay_period, business-day counters...). Environment.at(ts, tz=...) evaluates at any instant and timezone; extra={...} carries site-specific ambient values.

Loading rules from storage

from navrules.storages import FileStorage

async with FileStorage("payrate_rules.json") as storage:
    for spec in await storage.load():
        ruleset.add_rule(spec)
ruleset.compile()

AbstractStorage is the extension point for DB-backed definitions.

Development

# Python-only (fallback backend):
uv run --no-project --with pytest --with pytest-asyncio --with-editable . pytest tests

# Native backend:
make build-rust      # maturin develop --release
cargo test           # crate unit tests (rust/)
RUN_BENCH=1 pytest tests/benchmarks -s

The wheel is built with maturin (abi3-py311: one wheel covers CPython 3.11+). If the native extension cannot be imported, navrules silently runs on the pure-Python matcher — set NAVRULES_DISABLE_RUST=1 to force it.