Why async improves performance in FastAPI - See It in Action

Why async improves performance in FastAPI

📖 Scenario: You are building a simple web API using FastAPI. You want to understand how using asynchronous functions can help your API handle more requests efficiently.

🎯 Goal: Create a FastAPI app with a synchronous endpoint and an asynchronous endpoint. Learn how async functions improve performance by not blocking the server while waiting for slow tasks.

📋 What You'll Learn

Create a FastAPI app instance called app

Define a synchronous endpoint /sync that simulates a slow task using time.sleep(2)

Define an asynchronous endpoint /async that simulates a slow task using await asyncio.sleep(2)

Run the FastAPI app and observe how async endpoint allows handling multiple requests concurrently

💡 Why This Matters

🌍 Real World

Web APIs often need to handle many users at once. Using async lets the server work on other requests while waiting for slow tasks like database queries or network calls.

💼 Career

Understanding async in FastAPI is important for backend developers to build fast, scalable web services that can handle many users efficiently.

1

Create FastAPI app and synchronous endpoint

Import FastAPI and time. Create a FastAPI app instance called app. Define a synchronous GET endpoint /sync that waits 2 seconds using time.sleep(2) and returns the text 'Synchronous response'.

FastAPI

from fastapi import FastAPI
import time

app = FastAPI()

# Define synchronous endpoint /sync
# Your code here

Need a hint?

Use @app.get('/sync') decorator and define a normal function that calls time.sleep(2).

2

Add async endpoint configuration

Import asyncio. Define an asynchronous GET endpoint /async using async def that waits 2 seconds using await asyncio.sleep(2) and returns the text 'Asynchronous response'.

FastAPI

from fastapi import FastAPI
import time
import asyncio

app = FastAPI()

@app.get('/sync')
def sync_endpoint():
    time.sleep(2)
    return 'Synchronous response'

# Define asynchronous endpoint /async
# Your code here

Need a hint?

Use async def and await asyncio.sleep(2) inside the async endpoint function.

3

Explain async performance benefit with example

Add a comment above the async endpoint explaining that async allows the server to handle other requests while waiting. Also add a comment above the sync endpoint explaining it blocks the server during the wait.

FastAPI

from fastapi import FastAPI
import time
import asyncio

app = FastAPI()

# Your comment here about sync blocking
@app.get('/sync')
def sync_endpoint():
    time.sleep(2)
    return 'Synchronous response'

# Your comment here about async non-blocking
@app.get('/async')
async def async_endpoint():
    await asyncio.sleep(2)
    return 'Asynchronous response'

Need a hint?

Write clear comments above each endpoint explaining blocking vs non-blocking behavior.

4

Add code to run FastAPI app with uvicorn

Add the code to run the FastAPI app using uvicorn.run with app as the app instance, host as '127.0.0.1', and port 8000. Use the if __name__ == '__main__' guard.

FastAPI

from fastapi import FastAPI
import time
import asyncio
import uvicorn

app = FastAPI()

# This synchronous endpoint blocks the server for 2 seconds
@app.get('/sync')
def sync_endpoint():
    time.sleep(2)
    return 'Synchronous response'

# This asynchronous endpoint allows other requests during the 2 second wait
@app.get('/async')
async def async_endpoint():
    await asyncio.sleep(2)
    return 'Asynchronous response'

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

Need a hint?

Use if __name__ == '__main__': and call uvicorn.run with the correct parameters.