A web server is a program that listens for requests from clients (such as web browsers) and sends back responses (such as web pages, JSON data, or files). aiohttp is a library that provides asynchronous HTTP client and server functionality for Python. It allows you to write concurrent code using coroutines and the async/await syntax.

In this example-based, step-by-step tutorial, I will explain how to create a simple web server with aiohttp and Python. Without any further ado, let’s get started!

Table Of Contents

1 The Steps to Implement a Web Server

2 The Complete Code

The Steps to Implement a Web Server

Step 1: Install aiohttp:

pip install aiohttp

Then import web from the module:

from aiohttp import web

Step 2: Create an application object with the web.Application class:

app = aiohttp.web.Application()

Step 3: Define some routes and handlers

A route is a mapping between a URL path and a handler function that will process the request and return a response. A handler is a coroutine function that takes a request object as an argument and returns a response object.

In this example, we’ll define 2 routes

/: The root path. The corresponding handler function will return a simple HTML page.

/api: The API path. Its handler function will return some JSON data.

To register a route to the web server, we use the web.add_routes() method. Let’s see the code below for more clarity:

# Define a handler for the root path
async def root_handler(request):
    return web.Response(
        text="<h1>Welcome to Sling Academy!</h1>", content_type="text/html"
    )


# Add the root route and its handler to the app
app.add_routes([web.get("/", root_handler)])


# Define a handler for the /api path
async def api_handler(request):
    return web.json_response(
        {"status": 200, "message": "Welcome to the Sling Academy API!"}
    )


# Add the /api route and its handler to the app
app.add_routes([web.get("/api", api_handler)])

Step 4: Run the application using the aiohttp web server.

You can use the run_app() function from the aiohttp module to start the web server and run the application on a given host and port. For example, you can run the application on localhost and port 8080 like this:

aiohttp.web.run_app(app, host="localhost", port=8080)

The Complete Code

Here’s the final source code that combines all the steps we’ve seen in the previous section:

# SlingAcademy.com
# main.py

from aiohttp import web

# Create an instance of the web application
app = web.Application()


# Define a handler for the root path
async def root_handler(request):
    return web.Response(
        text="<h1>Welcome to Sling Academy!</h1>", content_type="text/html"
    )


# Add the root route and its handler to the app
app.add_routes([web.get("/", root_handler)])


# Define a handler for the /api path
async def api_handler(request):
    return web.json_response(
        {"status": 200, "message": "Welcome to the Sling Academy API!"}
    )


# Add the /api route and its handler to the app
app.add_routes([web.get("/api", api_handler)])

# Run the app
web.run_app(app, host="localhost", port=8080)

You execute the code like this: