# Durable Monty

> **⚠️ Experimental:** This is an experimental project exploring a different approach to durable functions. Not recommended for production use yet.

**Durable functions for Python.** Write normal `async/await` code that pauses at `gather()`, executes tasks in parallel (even distributed), and resumes when done.

## What Are Durable Functions?

Durable functions are workflows that survive crashes and restarts. Your code pauses when waiting for tasks, saves its state to a database, and resumes exactly where it left off when tasks complete - even if your process dies in between.

**Perfect for:** Long-running workflows, parallel task execution, distributed systems, background jobs.

## How It Works

Powered by [monty-python](https://github.com/pydantic/monty) - a sandboxed Python interpreter that can pause and serialize execution state. When your code hits `await gather()`, Monty captures the exact execution state (~800 bytes), returns pending tasks, and later resumes from that exact point with results.

**Result:** Pure Python async/await that works like Temporal or AWS Step Functions, but simpler.

### Why This Approach Is Simpler

**Other frameworks (Temporal, Durable Functions, etc.):**
- Re-execute your entire function from the start on every resume
- Use replay/event sourcing to return cached results for completed calls
- Example: If your workflow pauses at step 7, resuming re-runs steps 1-6 (with cached results) before continuing
- Requires deterministic code and careful side-effect management

**Durable Monty:**
- Serializes the exact Python execution state (call stack, variables, everything)
- No re-execution - just deserialize and continue from where you left off
- True pause/resume - no replay, no determinism requirements, no special coding patterns
- Simpler mental model: "save and restore" instead of "replay and cache"

**Trade-offs:**
- **Code versioning:** Changing workflow code can break in-flight executions (serialized state expects compatible code)
- **Migration complexity:** Updating workflows requires careful handling of existing executions
- **Less proven:** Built on [pydantic-monty](https://github.com/lix-tech/pydantic-monty), which is newer than battle-tested frameworks like Temporal
- **Python-only:** Requires deep interpreter integration, unlike replay-based systems that work with any language

The main practical challenge: if you iterate quickly on workflow code, in-flight executions may break on deployment. Consider draining executions before code changes or using versioned workflows.

```python
from durable_monty import init_db, OrchestratorService, Worker, LocalExecutor

def process(item):
    return f"processed_{item}"

code = """
from asyncio import gather
results = await gather(
    process('a'),
    process('b'),
    process('c')
)
results
"""

service = OrchestratorService(init_db())
# Pass function object - full path derived automatically
exec_id = service.start_execution(code, [process])

# Process until complete
worker = Worker(service, LocalExecutor())
worker.run(until_complete=True)

# Get the result
output = service.get_result(exec_id)
print(output)  # ['processed_a', 'processed_b', 'processed_c']
```

## Install

```bash
uv add durable-monty
```

## How It Works

1. Code hits `gather()` → pauses and saves state (~800 bytes)
2. Creates pending calls in database
3. Worker picks them up and executes in parallel
4. When all complete → resumes and returns result

State survives restarts. Parallel execution. Pure Python.

## Distributed Execution

**Redis Queue:**
```bash
uv add durable-monty --extra rq
```

```python
from durable_monty.executors.rq import RQExecutor

worker = Worker(service, RQExecutor())
worker.run()

# Start RQ workers: rq worker durable-monty
```

**Event-driven (Lambda, Modal):**
```bash
uv add durable-monty --extra api
```

```python
from durable_monty.api import create_app
import uvicorn

app = create_app(service)
uvicorn.run(app, port=8000)

# Executors POST results to: /webhook/complete
```

## Examples

- `examples/with_worker.py` - Local execution
- `examples/with_rq.py` - Redis Queue
- `examples/with_webhook.py` - Webhooks

## Development

```bash
git clone https://github.com/koenvo/monty-durable
cd monty-durable
uv sync
uv run pytest
```

## License

MIT
