Python SDK#

Use the Python SDK at a runtime boundary you own. This guide needs Python 3.10 or newer and the quickstart policy.

parse and resolve_file use (ok, value_or_error) tuples; parse_or_raise is the throwing variant. validate(...).is_valid is a property. check returns bool; gate returns an outcome with proceed. enforce raises HushSpecDenied before the handler.

Install and run the complete example#

Create an empty directory. Download these files, preserving the listed relative paths, and place policy.yaml at the top of that directory:

This example installs hushspec[signing]==1.0.0. The signing extra supplies the cryptography backend; without it, signing operations raise SigningUnavailable. On Windows activate the venv with .venv\Scripts\Activate.ps1 instead.

Terminal

python -m venv .venv
. .venv/bin/activate
python -m pip install -r requirements.txt
python main.py policy.yaml

Expected output: PASS: deny=0 dispatches; unconfirmed warn=0; confirmed warn=1; invalid policy refused. All effects are in a fresh temporary directory. No model API or credentials are required, and the program cleans up its own synthetic output.

Enforce before the effect#

The example parses and validates the policy, resolves it, and compiles it once. It then attaches a consistent actor and callback receipt sink to the guard. The synthetic handler creates one file only after enforcement permits dispatch.

main.pyDownload

from pathlib import Path
import sys
from tempfile import TemporaryDirectory
from trust import check_trust
from hushspec import (
    Actor, CallbackSink, EvaluationAction, HushGuard, compile_policy,
    parse_or_raise, resolve_file, validate,
)

policy_path = sys.argv[1] if len(sys.argv) > 1 else "policy.yaml"
document = parse_or_raise(Path(policy_path).read_text())
assert validate(document).is_valid
ok, resolved = resolve_file(policy_path)
assert ok, resolved
compiled = compile_policy(resolved)
check_trust(policy_path, resolved)
assert compiled.evaluate(EvaluationAction(type="tool_call", target="search")).decision.value == "allow"

receipts = []
options = dict(
    actor=Actor(agent_id="docs-agent", session_id="docs-session", principal="docs-user", runtime="docs/1.0.0"),
    sink=CallbackSink(receipts.append),
)
with TemporaryDirectory(prefix="hush-doc-effect-") as directory:
    output = Path(directory) / "effect.txt"
    dispatches = 0

    def dispatch(guard, tool):
        global dispatches
        outcome = guard.gate(EvaluationAction(type="tool_call", target=tool))
        if not outcome.proceed:
            return False
        with output.open("x") as file:
            file.write("confirmed once\n")
        dispatches += 1
        return True

    with HushGuard.from_file(policy_path, **options) as guard:
        assert not dispatch(guard, "deploy")
        assert not dispatch(guard, "write_file")
        assert dispatches == 0 and not output.exists()
    with HushGuard.from_file(policy_path, on_warn=lambda result, action: True, **options) as guard:
        assert dispatch(guard, "write_file")
        assert dispatches == 1
        assert output.read_text() == "confirmed once\n"
    assert receipts[-1].enforcement.outcome == "confirmed"
    assert receipts[-1].actor.agent_id == "docs-agent"
    try:
        HushGuard.from_yaml('hushspec: "1.0.0"\nunknown_rule: true\n')
    except ValueError:
        pass
    else:
        raise AssertionError("Invalid policy was accepted")
print("PASS: deny=0 dispatches; unconfirmed warn=0; confirmed warn=1; invalid policy refused")

The on_warn / onWarn callback in this demonstration approves one synthetic test action. A real integration must obtain approval from an authenticated channel and bind it to the pending action. Do not replace approval with unconditional true in a production agent.

Signing and keyrings#

The companion trust.py program is called by the main example. It creates an ephemeral test key, signs the resolved document, verifies with an explicit keyring, and rejects a different keyring. It prints no private key and does not persist one. Production signing identities belong to the operator.

Signing and verification must refer to the same resolved policy used for evaluation. See signing, bundles, and the exact signing APIs. A successful signature proves authenticity relative to your trust roots, not that a tool obeyed the policy.

Providers and reload#

HushGuard.from_provider(FileProvider(path)) loads once by default. Opt into watch=True or poll=True, not both. Use the guard as a context manager or call close() to stop its loop. Guard operations serialize. Confirmation handlers and custom sinks must not call or wait on the same guard.

Initial policy-load errors cannot fall back to a nonexistent policy. Ordinary guard reload preserves the last good policy on a rejected update and reports the error. It is not nonblocking: reload can wait for confirmation and receipt delivery. See hot reload for ordering and the distinct experimental coordinator refusal contract.

Receipts and failure handling#

The callback sink makes receipt contents visible to the test. It is not durable storage. Configure a chained file sink or another reviewed delivery path for operational evidence, and handle sink.error through an observer. A failed ordinary sink does not change the decision; if dispatch must require a durable permit, use the separately bounded experimental invocation workflow.

Receipts record actor fields, policy hash, decision, trace and enforcement outcome. They do not carry raw action content. The confirmed outcome distinguishes an approved warning from a plain allow.

API map and next steps#

The SDK API contract covers parse/validate, resolve/merge, compile/evaluate, actors, receipts, sinks, signing, keyrings, providers, panic mode and error conventions. For mapping effects, read MCP and runtime integration. Use conformance to understand what a test corpus establishes; this example is an integration regression, not an independent conformance certificate.