Python SDK Error Handling

Overview

The Python SDK uses ApplicationError for application-specific errors and provides comprehensive retry policy configuration. Generally, the following information about errors and retryability applies across activities, child workflows and Nexus operations.

Application Errors

from temporalio import activity
from temporalio.exceptions import ApplicationError

@activity.defn
async def validate_order(order: Order) -> None:
    if not order.is_valid():
        raise ApplicationError(
            "Invalid order",
            type="ValidationError",
        )

Non-Retryable Errors

from dataclasses import dataclass
from temporalio import activity
from temporalio.exceptions import ApplicationError

@dataclass
class ChargeCardInput:
    card_number: str
    amount: float

@activity.defn
async def charge_card(input: ChargeCardInput) -> str:
    if not is_valid_card(input.card_number):
        raise ApplicationError(
            "Permanent failure - invalid credit card",
            type="PaymentError",
            non_retryable=True,  # Will not retry activity
        )
    return await process_payment(input.card_number, input.amount)

Handling Activity Errors

from datetime import timedelta
from temporalio import workflow
from temporalio.exceptions import ActivityError, ApplicationError

@workflow.defn
class MyWorkflow:
    @workflow.run
    async def run(self) -> str:
        try:
            return await workflow.execute_activity(
                risky_activity,
                start_to_close_timeout=timedelta(minutes=5),
            )
        except ActivityError as e:
            workflow.logger.error(f"Activity failed: {e}")
            # Handle or re-raise
            raise ApplicationError("Workflow failed due to activity error")

Retry Policy Configuration

from datetime import timedelta
from temporalio import workflow
from temporalio.common import RetryPolicy

@workflow.defn
class MyWorkflow:
    @workflow.run
    async def run(self) -> str:
        result = await workflow.execute_activity(
            my_activity,
            start_to_close_timeout=timedelta(minutes=10),
            retry_policy=RetryPolicy(
                maximum_interval=timedelta(minutes=1),
                maximum_attempts=5,
                non_retryable_error_types=["ValidationError", "PaymentError"],
            ),
        )
        return result

Only set options such as maximum_interval, maximum_attempts etc. if you have a domain-specific reason to. If not, prefer to leave them at their defaults.

Timeout Configuration

from datetime import timedelta
from temporalio import workflow

@workflow.defn
class MyWorkflow:
    @workflow.run
    async def run(self) -> str:
        return await workflow.execute_activity(
            my_activity,
            start_to_close_timeout=timedelta(minutes=5),      # Single attempt
            schedule_to_close_timeout=timedelta(minutes=30),  # Including retries
            heartbeat_timeout=timedelta(minutes=2),          # Between heartbeats
        )

Workflow Failure

from temporalio import workflow
from temporalio.exceptions import ApplicationError

@workflow.defn
class MyWorkflow:
    @workflow.run
    async def run(self) -> str:
        if some_condition:
            raise ApplicationError(
                "Cannot process order",
                type="BusinessError",
            )
        return "success"

Note: Do not use non_retryable= with ApplicationError inside a worklow (as opposed to an activity).

Best Practices

Use specific error types for different failure modes
Mark permanent failures as non-retryable
Configure appropriate retry policies
Log errors before re-raising
Use ActivityError to catch activity failures in workflows
Design code to be idempotent for safe retries (see more at references/core/patterns.md)

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