Dbos Python

---
name: dbos-python
description: DBOS Python SDK for building reliable, fault-tolerant applications with durable workflows. Use this skill when writing Python code with DBOS, creating workflows and steps, using queues, using DBOSClient from external applications, or building applications that need to be resilient to failures.
risk: safe
source: https://docs.dbos.dev/
license: MIT
metadata:
  author: dbos
  version: "1.0.0"
  organization: DBOS
  date: January 2026
  abstract: Comprehensive guide for building fault-tolerant Python applications with DBOS. Covers workflows, steps, queues, communication patterns, and best practices for durable execution.
---

# DBOS Python Best Practices

Guide for building reliable, fault-tolerant Python applications with DBOS durable workflows.

## When to Use

Reference these guidelines when:
- Adding DBOS to existing Python code
- Creating workflows and steps
- Using queues for concurrency control
- Implementing workflow communication (events, messages, streams)
- Configuring and launching DBOS applications
- Using DBOSClient from external applications
- Testing DBOS applications

## Rule Categories by Priority

| Priority | Category | Impact | Prefix |
|----------|----------|--------|--------|
| 1 | Lifecycle | CRITICAL | `lifecycle-` |
| 2 | Workflow | CRITICAL | `workflow-` |
| 3 | Step | HIGH | `step-` |
| 4 | Queue | HIGH | `queue-` |
| 5 | Communication | MEDIUM | `comm-` |
| 6 | Pattern | MEDIUM | `pattern-` |
| 7 | Testing | LOW-MEDIUM | `test-` |
| 8 | Client | MEDIUM | `client-` |
| 9 | Advanced | LOW | `advanced-` |

## Critical Rules

### DBOS Configuration and Launch

A DBOS application MUST configure and launch DBOS inside its main function:

```python
import os
from dbos import DBOS, DBOSConfig

@DBOS.workflow()
def my_workflow():
    pass

if __name__ == "__main__":
    config: DBOSConfig = {
        "name": "my-app",
        "system_database_url": os.environ.get("DBOS_SYSTEM_DATABASE_URL"),
    }
    DBOS(config=config)
    DBOS.launch()
```

### Workflow and Step Structure

Workflows are comprised of steps. Any function performing complex operations or accessing external services must be a step:

```python
@DBOS.step()
def call_external_api():
    return requests.get("https://api.example.com").json()

@DBOS.workflow()
def my_workflow():
    result = call_external_api()
    return result
```

### Key Constraints

- Do NOT call `DBOS.start_workflow` or `DBOS.recv` from a step
- Do NOT use threads to start workflows - use `DBOS.start_workflow` or queues
- Workflows MUST be deterministic - non-deterministic operations go in steps
- Do NOT create/update global variables from workflows or steps

## How to Use

Read individual rule files for detailed explanations and examples:

```
references/lifecycle-config.md
references/workflow-determinism.md
references/queue-concurrency.md
```

## References

- https://docs.dbos.dev/
- https://github.com/dbos-inc/dbos-transact-py