Async vs sync decision in FastAPI - Hands-On Comparison

Async vs Sync Decision in FastAPI

📖 Scenario: You are building a simple web API using FastAPI. You want to understand how to write endpoints that handle requests either synchronously or asynchronously. This helps your API respond efficiently depending on the task.

🎯 Goal: Create a FastAPI app with two endpoints: one synchronous and one asynchronous. Learn how to define each type and see how FastAPI handles them.

📋 What You'll Learn

Create a FastAPI app instance named app

Write a synchronous endpoint /sync that returns a greeting message

Write an asynchronous endpoint /async that returns a greeting message

Use async def for the async endpoint and def for the sync endpoint

💡 Why This Matters

🌍 Real World

Web APIs often need to handle tasks that can be done quickly or tasks that wait for other services. Knowing when to use async or sync helps make APIs faster and more efficient.

💼 Career

FastAPI is popular for building modern web APIs. Understanding async vs sync endpoints is important for backend developers to write scalable and responsive services.

1

Create FastAPI app instance

Import FastAPI from fastapi and create an app instance called app.

FastAPI

# Import FastAPI and create app instance
# Your code here

Need a hint?

Use from fastapi import FastAPI and then app = FastAPI().

2

Add synchronous endpoint

Add a synchronous endpoint /sync using @app.get("/sync") and a function named sync_endpoint that returns the dictionary {"message": "Hello from sync"}.

FastAPI

from fastapi import FastAPI

app = FastAPI()

# Add synchronous endpoint /sync here
# Your code here

Need a hint?

Use @app.get("/sync") decorator and define a normal def function.

3

Add asynchronous endpoint

Add an asynchronous endpoint /async using @app.get("/async") and a function named async_endpoint defined with async def that returns the dictionary {"message": "Hello from async"}.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/sync")
def sync_endpoint():
    return {"message": "Hello from sync"}

# Add asynchronous endpoint /async here
# Your code here

Need a hint?

Use async def to define the async endpoint function.

4

Run FastAPI app with Uvicorn

Add the code block to run the FastAPI app with Uvicorn when the script is executed directly. Use if __name__ == "__main__" and call uvicorn.run(app, host="127.0.0.1", port=8000). Import uvicorn at the top.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/sync")
def sync_endpoint():
    return {"message": "Hello from sync"}

@app.get("/async")
async def async_endpoint():
    return {"message": "Hello from async"}

# Add code to run app with uvicorn here
# Your code here

Need a hint?

Import uvicorn and use the if __name__ == "__main__" block to run the app.