Build a Simple Python Web Server from Scratch – Step‑by‑Step Guide

Motivation

Re‑implementing a network server from scratch helps developers understand how the components of a modern software stack—languages, compilers, databases, operating systems, network protocols, and web frameworks—fit together.

What Is a Network Server?

A network server is a program that runs on a physical machine, creates a listening socket, accepts incoming TCP connections, parses HTTP requests, and sends HTTP responses. Clients can be browsers or any HTTP‑capable software.

Minimal Python Server

The following Python script implements a very small HTTP server that listens on port 8888 and returns Hello, World! for the path /hello. Save it as webserver1.py and run it from the command line.

import socket

HOST = ''          # Listen on all interfaces
PORT = 8888

# Create a TCP socket and bind it to the address
listen_sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
listen_sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
listen_sock.bind((HOST, PORT))
listen_sock.listen(5)
print('Listening on port', PORT)

while True:
    client_sock, client_addr = listen_sock.accept()
    request = client_sock.recv(1024).decode('utf-8')
    # Simple handling: always respond with the same message
    response = ('HTTP/1.1 200 OK
'
                'Content-Type: text/plain; charset=utf-8
'
                '
'
                'Hello, World!')
    client_sock.sendall(response.encode('utf-8'))
    client_sock.close()

Run the server: python webserver1.py Then open a browser and navigate to http://localhost:8888/hello. The page should display Hello, World!

Understanding URLs and TCP Connections

A URL (Uniform Resource Locator) tells a client which host and which resource to request. Before an HTTP request is sent, the client establishes a TCP connection to the server’s IP address and port using a socket.

Manual Request with Telnet

You can simulate a browser with the telnet command: telnet localhost 8888 After the connection is open, type the request line and press Enter twice: GET /hello HTTP/1.1 The server will reply with the same HTTP response shown above.

HTTP Request and Response Structure

An HTTP request line consists of three parts:

Method (e.g., GET)

Path (e.g., /hello)

Protocol version (e.g., HTTP/1.1)

The corresponding response starts with a status line, followed by a blank line and the body:

HTTP/1.1 200 OK

Hello, World!

In this minimal server the request is not parsed; any data sent by the client results in the same static response.

Summary of Server Operation

Create a listening socket on the desired port.

Enter an infinite loop that accept() s new connections.

Read the incoming bytes (the HTTP request).

Send a fixed HTTP response containing a status line, required headers, a blank line, and the response body.

Close the client socket and wait for the next connection.

This implementation can be tested with a web browser, curl, or telnet. It demonstrates the core workflow of a web server without any external dependencies.

Challenge

Without modifying webserver1.py, devise a way to run applications built with Django, Flask, and Pyramid on the same server, satisfying each framework’s requirements. The solution is explored in the next part of the series.