Yosoi Python SDK

Yosoi's Python package provides Pydantic authoring and typed outcomes over the public Rust SDK. The surface includes browser Flows and owned Session/Work contexts, documents, locator plans, typed Contracts, policy, asynchronous Requests, Map, Search, and caller-controlled cancellation. Rust parses and locates documents, groups raw Contract evidence, acquires URLs, discovers candidates, and validates Policy. Python Contracts construct and validate their records through Pydantic. Cross-language parity is tracked per public item; this package does not claim complete verified parity.

Pydantic models describe inputs and result values. The packaged PyO3 extension calls the public Rust SDK for native processing. Python Contract fields use ordinary Pydantic types, defaults, aliases, constraints, validators, and serializers. Python objects also hold native handles; for example, a parsed document can be reused and closed explicitly or with a context manager. Pydantic 2 is the only declared Python runtime dependency; the native extension is part of the package.

Start with the runnable review examples to inspect Rust policy defaults, Contract schemas and evidence, local HTTP workflows, and network outcomes. The browser beta example shows Flows built from caller-supplied site actions, Contract plans, and typed expectations without embedding site selectors.

Browser beta API

Build immutable action sequences with ys.flow([...]), then call await flow.invoke() for a managed browser or await flow.invoke(work) to borrow an acquired Work lease. flow.bind(policy).invoke() applies an explicit validated Yosoi Policy. FlowOutcome.require_completed() returns the original outcome when every step completes and raises FlowExecutionError with that same outcome for failed, cancelled, unknown, or issue-bearing execution. Native invocation failures that include partial execution or cleanup details raise FlowInvocationError with those facts attached.

The flow policy retains Rust's Continue defaults when on_failure and on_cancellation are omitted. That is useful for independent steps; workflows with dependent side effects should stop after a failed assertion. The flat ys.flow(...) factory accepts explicit timeout, continuation, and failure capture settings:

checkout = ys.flow(
    steps,
    timeout_ms=30_000,
    on_failure=ys.policy.Stop(scope="invocation"),
    on_cancellation=ys.policy.Stop(scope="invocation"),
)

ys.session(...) creates an async context manager that owns the browser Session. Its work() context manager borrows control; Work release does not close the Session, and leaving the Session context closes it. JavaScript evaluation needs an explicit managed Flow grant with .allow_javascript(); both flow.allow_javascript().bind(policy) and flow.bind(policy).allow_javascript() keep that grant on the managed Flow. For a borrowed Work lease, grant it through the owning SessionPolicy(allow_arbitrary_js=True) and the allowed action list; a Flow grant cannot elevate that Session's policy.

ys.request.new(url).in_session(session).send() uses the retained Session's browser request policy. .with_work(work) sends on an existing borrowed Work lease, and .bind(policy) keeps an explicit Policy when either owner is selected. These request wrappers leave Session and Work cleanup with their caller and return the same typed Response with its document outcomes.

ys.evaluate_file(path), ys.run_module(path), and ys.run_module_with_export(path, name) synchronously snapshot and validate source before invocation. Files are bounded UTF-8 source. Module imports must form a bounded relative local graph; remote, absolute, bare, and computed dynamic imports are rejected. Selected exports are read as JSON after evaluation and are not invoked.

Typed ys.assert_all(Contract, plan=..., checks=[...]) assembles one immediate Contract observation, constructs its Python model through Pydantic, and runs all synchronous predicates against that record. Attach .until() or pass the assertion to ys.until(...) when bounded polling is intended. Callback exceptions remain visible as structured check errors; async predicates and non-boolean results are rejected. Serialized assertion descriptors contain no Python code, so a Flow loaded from a persisted descriptor must be rebuilt with its local checks before invocation.

This Python surface does not expose Watch streams, additional tab creation, or remote browser attachment. The example accepts site-specific actions, expectations, Plans, and Contracts from the caller; it does not discover or certify a website automatically.

The earlier compatibility report records a local wheel matrix for the pre-Contract SDK snapshot. It does not verify the current Contract binding, CPython 3.14.8t, browser execution, all release platforms, or live Search providers. The public compatibility page records the current evidence boundary.

Interpreter targets and wheels

The package declares >=3.12,<3.16 and requires Pydantic >=2.14,<3. Its interpreter targets are normal CPython 3.12–3.15, plus free-threaded CPython 3.14.8t and 3.15.0t.

The native extension uses interpreter-specific wheels: cp312, cp313, cp314, cp314t, cp315, and cp315t. These ABI tags do not promise a wheel for every operating system or architecture. Check the artifacts for the release and platform you plan to install.

Python CI is configured for all six targets. For each target it builds a wheel from an sdist, installs that wheel, runs package checks, and requests the policy, locate, contracts, and local examples. Workflow configuration is not evidence of a completed hosted run or of published wheels for all platforms. Local Search examples do not certify live providers.

Local workflow

Install one selected interpreter and the locked development environment from the repository root. Substitute 3.13, 3.14, or the exact 3.14.8t, 3.15.0, or 3.15.0t selector to work with another target:

uv python install 3.12 3.13 3.14 3.14.8t 3.15.0 3.15.0t
uv sync --locked --python 3.12

For package checks that build and install a wheel from an sdist:

uv sync --locked --no-install-project --python 3.12
uv run --no-sync ruff check python
uv run --no-sync ruff format --check python
uv run --no-sync ty check python
interpreter=$(uv run --no-sync python -c 'import os, sys; print(os.path.realpath(sys.executable))')
CARGO_BUILD_JOBS=1 uv build --no-build-isolation --config-setting="build-args=--interpreter=$interpreter"
uv pip install --python .venv/bin/python --reinstall dist/*.whl
uv run --no-sync pytest

The build command produces an sdist and builds the wheel from it with the locked development tools. Source builds need the Rust toolchain and native build prerequisites. Use one Cargo worker. For iterative binding work, uv sync --locked --python <interpreter> builds an editable installation. The explicit resolved interpreter path keeps the normal and free-threaded ABIs distinct when switching the project environment with a shared Cargo target directory.