Reference¶

Back to Stream Handling Overview

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Incremental Processing¶

Streaming handlers process items one at a time, yielding results as they become available. This allows clients to receive progress updates in real-time.

Event Emission¶

After each yield, events are collected and can be emitted. Events are processed after each yield, allowing for parallel processing of side effects.

Parallel Event Processing¶

Events can be processed concurrently with configurable concurrency limits. This improves performance when multiple event handlers need to process events independently.

SSE Integration¶

Streaming handlers work seamlessly with Server-Sent Events (SSE) in FastAPI, enabling real-time progress updates in web applications.

Streaming handlers are ideal for:

Batch processing — Processing large batches of items with progress updates
File uploads — Processing uploaded files one by one
Data import — Importing data with real-time progress
Long-running operations — Operations that take time and benefit from progress updates
Real-time updates — Applications that need to show progress to users
Clear events after processing — Implement clear_events() to prevent event accumulation
Use appropriate concurrency limits — Set max_concurrent_event_handlers based on your resource constraints
Handle errors gracefully — Wrap streaming logic in try-except blocks
Yield meaningful results — Include progress information in response objects
Use SSE for web applications — Stream results via SSE for better user experience

Feature	Regular Handler	Streaming Handler
Response	Single response	Multiple responses (yielded)
Processing	All at once	Incremental
Progress Updates	Not available	Real-time
Event Processing	After completion	After each yield
Use Case	Simple operations	Batch/long-running operations