Let us see what options are available under Python. In Python, a socket can be placed in the blocking or non-blocking mode. In the non-blocking mode, if any call to API, for example, send() or recv(), encounters any problem, an error will be raised. However, in the blocking mode, this will not stop the operation. We can create a normal TCP socket and experiment with both the blocking and non-blocking operations.

In order to manipulate the socket's blocking nature, we need to create a socket object first.

We can then call setblocking(1) to set up blocking or setblocking(0) to unset blocking. Finally, we bind the socket to a specific port and listen for incoming connections.

Listing 1.9 shows how the socket changes to blocking or non-blocking mode as follows:

#!/usr/bin/env python
# Python Network Programming Cookbook -- Chapter - 1
# This program is optimized for Python 2.7. It may run on any
# other Python version with/without modifications

import socket

def test_socket_modes():
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.setblocking(1)
    s.settimeout(0.5)
    s.bind(("127.0.0.1", 0))
    
    socket_address = s.getsockname()
    print "Trivial Server launched on socket: %s" %str(socket_address)
    while(1):
        s.listen(1)

if __name__ == '__main__':
    test_socket_modes()

If you run this recipe, it will launch a trivial server that has the blocking mode enabled as shown in the following command:

$ python 1_9_socket_modes.py 
Trivial Server launched on socket: ('127.0.0.1', 51410)

In this recipe, we enable blocking on a socket by setting the value 1 in the setblocking() method. Similarly, you can unset the value 0 in this method to make it non-blocking.

This feature will be reused in some later recipes, where its real purpose will be elaborated.