PYTHON NETWORKING - Complete Guide For Python Programming (2015)

Complete Guide For Python Programming (2015)

PYTHON NETWORKING

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.

What are Sockets?

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.

Sockets have their own vocabulary:

The socket Module:

To create a socket, you must use the socket.socket() function available in socket module. Syntax:

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

Description of parameters:

socket_family: This is either AF_UNIX or AF_INET, as explained earlier.

socket_type: This is either SOCK_STREAM or SOCK_DGRAM.

protocol: This is usually left out, defaulting to 0.

Socket objects are use required functions to create your client or server program. Here I am going to share with you the list of functions required:

Server Socket Methods:

Client Socket Methods:

General Socket Methods:

A Simple Server:

To write Internet servers, we use the socket function available in socket module to create a socket object. A socket object is then used to call other functions to set up 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.

Example:

#!/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 = 102 # 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('Thanks for connecting')

c.close() # Close the connection

A Simple Client:

Now, we will write a very simple client program, which will open a connection to a given port 102 and given host. This is very simple to create a socket client using Python's socket module function. The socket.connect(hosname, 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, remember 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:

Example:

#!/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 = 102 # 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.

# Following would start a server in background.

$ python server.py &

# Once server is started run client as follows:

$ python client.py

Output:

Got connection from ('127.0.0.1', 48437)

Thanks for connecting

Python Internet modules

Here below is a list of some important modules, which are used in Python Network/Internet programming.