Python Networking

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Python provides two levels of access to network services. At a low level, you can access the basic socket support in the underlying operating system, which allows you to implement clients and servers for both connection-oriented and connectionless protocols.

Python also has libraries that provide higher-level access to specific application-level network protocols, such as FTP, HTTP, and so on.

This chapter gives you understanding on most famous concept in Networking - Socket Programming.

What is Socket?

Sockets are the endpoints of a bidirectional communications channel. Sockets may communicate within a process, between processes on the same machine, or between processes on different continents.

Sockets may be implemented over a number of different channel types: Unix domain sockets, TCP, UDP, and so on. The socket library provides specific classes for handling the common transports as well as a generic interface for handling the rest.

Socket Module

To create a socket, you must use the socket.socket() function available in socket module, which has the general syntax:

s = socket.socket (socket_family, socket_type, protocol=0)

Server Socket Method

Client Socket Method

General Socket Methods

#!/usr/bin/python # This is server.py file

import socket # Import socket module

s = socket.socket() # Create a socket object
host = socket.gethostname() # Get local machine name
port = 12345 # Reserve a port for your service.
s.bind((host, port)) # Bind to the port

s.listen(5) # Now wait for client connection.
while True:
  c, addr = s.accept() # Establish connection with client.
  print ('Got connection from', addr)
  c.send('Thank you for connecting')
  c.close() # Close the connection

Simple Server

To write an Internet server, we use the socket function available in socket module to create a socket object. The socket object is then used to call other functions to setup a socket server.

Now call bind(hostname,port) function to specify a port for your service on the given host.

Next, call the accept method of the returned object. This method waits until a client connects to the port you specified, and then returns a connection object that represents the connection to that client.

Simple Client

Let us write a very simple client program which opens a connection to a given port 12345 and a given host. This is very simple to create a socket client using the Python's socket module function.

The socket.connect(hostname, port) opens a TCP connection to hostname on the port. Once you have a socket open, you can read from it like any IO object. When done, do not forget to close it, as you would close a file.

The following code is a very simple client that connects to a given host and port, reads any available data from the socket, and then exits:

#!/usr/bin/python # This is client.py file

import socket # Import socket module

s = socket.socket() # Create a socket object
host = socket.gethostname() # Get local machine name
port = 12345 # Reserve a port for your service.

s.connect((host, port))
print (s.recv(1024))
s.close # Close the socket when done

Now run this server.py in background and then run above client.py to see the result.

Run server:

python server.py &

After server runs, continue

Run client:

python client.py

The result will be like this : Got connection from ('127.0.0.1', 48437) Thank you for connecting

Python Internet Modules

Here is a list of some important modules in Python Network / Internet programming.

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