How can I implement a simple web server using Python without using any libraries?

I need to implement a very simple web-server-like app in Python which would perform basic HTTP requests and responses and display very basic output on the web page. I am not too concerned about actually coding it in Python, but I am not sure where to start? How to set this up? One file? Multiple files? I guess I have no idea how to approach the fact that this is a "server" - so I am unfamiliar with how to approach dealing with HTTP requests/sockets/processing requests, etc. Any advice? Resources?

Solution

You can use socket programming for this purpose. The following snippet creates a tcp socket and listens on port 9000 for http requests:

from socket import *

def createServer():
    serversocket = socket(AF_INET, SOCK_STREAM)
    serversocket.bind(('localhost',9000))
    serversocket.listen(5)
    while(1):
        (clientsocket, address) = serversocket.accept()
        clientsocket.send("HTTP/1.1 200 OK\n"
         +"Content-Type: text/html\n"
         +"\n" # Important!
         +"<html><body>Hello World</body></html>\n")
        clientsocket.shutdown(SHUT_WR)
        clientsocket.close()

    serversocket.close()

createServer()

Start the server, $ python server.py. Open http://localhost:9000/ in your web-browser (which acts as client). Then in the browser window, you can see the text "Hello World" (http response).

EDIT** The previous code was only tested on chrome, and as you guys suggested about other browsers, the code was modified as:

To make the response http-alike you can send in plain header with http version 1.1, status code 200 OK and content-type text/html.
The client socket needs to be closed once response is submitted as it's a TCP socket.
To properly close the client socket, shutdown() needs to be called socket.shutdown vs socket.close

Then the code was tested on chrome, firefox (http://localhost:9000/) and simple curl in terminal (curl http://localhost:9000).