---name: dbos-pythondescription: DBOS Python SDK (3.x) for building reliable, fault-tolerant applications with durable workflows. Use this skill when writing Python code with DBOS, creating workflows and steps, using queues, datasource transactions, or schedules, using DBOSClient from external applications, upgrading DBOS Python 2.x code to 3.x, or building applications that need to be resilient to failures.license: MITmetadata: author: dbosversion: 2.0.0organization: DBOSdate: September 2026abstract: 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. Targets DBOS Python 3.x.

When to Apply

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
• Upgrading DBOS Python 2.x code to 3.x

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:

import os
from dbos import DBOS, DBOSConfig

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

if __name__ == "__main__":
    config: DBOSConfig = {
        "name": "my-app",
        "application_version": "0.1.0",
        "system_database_url": os.environ.get("DBOS_SYSTEM_DATABASE_URL"),
    }
    DBOS(config=config)
    DBOS.launch()

When creating a new application, set application_version to "0.1.0". If omitted, DBOS derives an opaque hash from workflow source code. When editing an existing application, leave its configured version alone — changing it is a deployment decision (see references/advanced-versioning.md).

Workflow and Step Structure

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

@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
• In async def code, use the _async variants of DBOS methods (await DBOS.start_workflow_async(...), send_async, recv_async, sleep_async, register_queue_async, ...): many synchronous DBOS methods (such as DBOS.sleep, DBOS.recv, DBOS.send, DBOS.set_event, DBOS.get_event, and DBOS.register_queue) raise RuntimeError when called while an event loop is running
• Register queues and create schedules AFTER DBOS.launch(); create datasources BEFORE it

Removed in DBOS 3.0 (never generate these)

@DBOS.transaction / DBOS.sql_session / application_database_url (use datasources), Queue(...) (use DBOS.register_queue), partition_queue / priority_enabled, @DBOS.scheduled (use DBOS.apply_schedules), and DBOS(fastapi=...) / DBOS(flask=...). To migrate existing 2.x code, see references/advanced-upgrading-v3.md.

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/advanced-upgrading-v3.md
references/advanced-shared-database.md

If multiple applications share one system database, see references/advanced-shared-database.md.

References

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