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FastAPI Event Emitter

  The FastAPIEventEmitter provides a powerful way to build reactive FastAPI applications using an event-driven architecture. It leverages FastAPI's asynchronous BackgroundTasks to handle events outside the request-response cycle.

What is it?

  The FastAPIEventEmitter is a concrete implementation of the EventEmitter class that utilizes FastAPI's BackgroundTasks for event handling. It provides a convenient way to incorporate event-driven functionality into FastAPI applications, allowing you to implement tasks such as sending emails in a decoupled and asynchronous manner.

How it Works

  The FastAPIEventEmitter handles the emission and processing of events by utilizing the FastAPI's background tasks queue. When an event is emitted, its execution is scheduled into the FastAPI's background tasks to run asynchronously after the response is sent.

Usage

To start using the FastAPIEventEmitter, follow these steps:

  1. Install Dependencies: Ensure FastAPI and Pyventus are installed.

  2. Dependency injection and usage: The FastAPIEventEmitter integrates fully with FastAPI and can be used in routes or elsewhere via dependency injection. As an example, we'll create a simple FastAPI app to simulate a non-blocking email notification. Create a main.py file and add the following code:

    main.py
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    import time
from typing import Dict

from fastapi import FastAPI, Depends

from pyventus import EventLinker
from pyventus.emitters.fastapi import FastAPIEventEmitter


@EventLinker.on("SendEmail")
def event_callback(email: str):
    print(f"Sending email to: {email}")
    time.sleep(2)
    print("Email sent successfully!")


app = FastAPI()

@app.get("/")
async def send_email(
    event_emitter: FastAPIEventEmitter = Depends(FastAPIEventEmitter),
) -> Dict[str, str]:
    event_emitter.emit("SendEmail", "email@pyventus.com")
    return {"message": "Email sent!"}
    main.py
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    import time
from typing import Dict

from fastapi import FastAPI, Depends

from pyventus import EventLinker
from pyventus.emitters.fastapi import FastAPIEventEmitter


@EventLinker.on("SendEmail")
def event_callback(email: str):
    print(f"Sending email to: {email}")
    time.sleep(2)
    print("Email sent successfully!")


app = FastAPI()

@app.get("/")
async def send_email(
    event_emitter: FastAPIEventEmitter = Depends(FastAPIEventEmitter.options(debug=False)),
) -> Dict[str, str]:
    event_emitter.emit("SendEmail", "email@pyventus.com")
    return {"message": "Email sent!"}

  3. Run the server: Start the app with:

    uvicorn main:app --reload

    Open your browser at http://127.0.0.1:8000/. You will see the JSON response as:

    { "message": "Email sent!" }

    You'll also be able to see the outputs of the functions in the console logs as follows:

    INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [28720]
INFO:     Started server process [28722]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     127.0.0.1:57926 - "GET / HTTP/1.1" 200 OK

Sending email to: email@pyventus.com
Email sent successfully!

Recap

  As we have seen, the FastAPIEventEmitter allows building reactive FastAPI apps using an event-driven architecture. By leveraging background tasks, events can be emitted from routes and processed independently without blocking responses. This delivers asynchronous and non-blocking behavior for tasks like emails, jobs, streams and more. The emitter integrates seamlessly with FastAPI via dependency injection.