State Machine v0.3.0

A lightweight, type-safe Python state machine implementation using modern Python 3.13+ features like PEP 695 type parameters.

Features

• Type Safety: Leverage Python's type system to ensure consistent states, events, and contexts.
• Decorator Support: Easily define transitions using the @sm.transition decorator.
• Auditing: Built-in support for recording transition history via AuditedStateMachine and AuditContext.
• Flexible Context: Pass a custom context object to transition actions to maintain state outside the machine.

Installation

This project uses uv for dependency management. To get started, ensure you have uv installed and run:

uv sync

You can install the package via pip:

pip install semantic-state-machine

Usage

Basic State Machine

Define your states and events as Enums and create a context class.

from enum import Enum
from semantic_state_machine import StateMachine

class State(Enum):
    LOCKED = 1
    UNLOCKED = 2

class Event(Enum):
    PUSH = 1
    COIN = 2

class TurnstileContext:
    def __init__(self):
        self.total_coins = 0

sm = StateMachine[State, Event, TurnstileContext]()

@sm.transition(State.LOCKED, Event.COIN, State.UNLOCKED)
def insert_coin(ctx: TurnstileContext) -> None:
    ctx.total_coins += 1
    print("Coin inserted. Turnstile unlocked.")

@sm.transition(State.UNLOCKED, Event.PUSH, State.LOCKED)
def push_turnstile(ctx: TurnstileContext) -> None:
    print("Turnstile pushed. Turnstile locked.")

# Usage
ctx = TurnstileContext()
current_state = State.LOCKED
current_state = sm.handle_transition(ctx, current_state, Event.COIN)
# current_state is now State.UNLOCKED

Audited State Machine

Use AuditedStateMachine and AuditContext to automatically track the history of transitions.

from semantic_state_machine import AuditedStateMachine, AuditContext

class MyContext(AuditContext[State, Event]):
    pass

sm = AuditedStateMachine[State, Event, MyContext]()

# Transitions are defined the same way
@sm.transition(State.LOCKED, Event.COIN, State.UNLOCKED)
def insert_coin(ctx: MyContext):
    pass

ctx = MyContext()
sm.handle_transition(ctx, State.LOCKED, Event.COIN)

# The transition is automatically recorded
print(ctx.audit_trail())  # [(State.LOCKED, Event.COIN)]

# Example of a custom audit trail formatter (e.g., counting transitions)
transition_count = ctx.audit_trail(lambda trail: len(trail))
print(f"Total transitions: {transition_count}")  # Total transitions: 1

Testing

The project includes a comprehensive suite of unit and integration tests.

Run All Tests

uv run pytest tests/

Run with Coverage

uv run pytest --cov=src tests/

The current implementation maintains 100% code coverage across the core logic and integration workflows.

Project Structure

• src/semantic_state_machine/: Core implementation.
• tests/unit/: Focused unit tests for individual components.
• tests/integration/: End-to-end workflow simulations.
• tests/hypothesis/: Property-based tests for robust edge-case discovery.

Development Standards

This project adheres to professional, type-safe development practices:

• Pre-commit: We enforce linting (ruff), formatting (ruff-format), and type checking (ty) using pre-commit hooks.
• Tiered Testing:
  • Fast Lane: Unit and integration tests run on every commit via the check CI job.
  • Robustness Lane: Property-based fuzzing using hypothesis executes during Pull Requests to uncover edge cases.
• CI/CD: The pipeline is configured to enforce quality, with static analysis and fast tests acting as a gateway for property-based robustness testing.