Python Network Programming


Contents

Python delivers two levels of right to network services. At a low level, you can access the elementary socket reinforcing in the underlying operating system, which authorizes you to utilize clients and servers for both connection-oriented and connection less protocols. Python is loaded with wide libraries supplying exact protocols like FTP, HTTP, etc high-level applicationnetwork programming. This chapter delivers you understanding on most illustrious concept in Networking - Socket Programming.

What is Sockets?

Sockets are considered as the last points of a bi-directional statements channel. Sockets might converse within a procedure, between courses on the aforementioned machine, or amid processes on dissimilar continents.

Sockets might be put into practiced over several assorted channel kinds: Unix domain sockets, TCP, UDP, etc. The socket library offers exact classes for running the ordinary transports and a general interface for managing the rest.

Sockets have their own vocabulary −

Sr.No.

Term & Description

1

Domain

The family of protocols that is used as the transport mechanism. These values are constants such as AF_INET, PF_INET, PF_UNIX, PF_X25, and so on.

2

type

The type of communications between the two endpoints, typically SOCK_STREAM for connection-oriented protocols and SOCK_DGRAM for connection-less protocols.

3

protocol

Typically zero, this may be utilized to identify a variable of a protocol within a domain and type.

4

hostname

The identifier of a network interface −

· 

A string, which can be a host name, a dotted-quad address, or an IPV6 address in colon (and possibly dot) notation

· 

· 

A string "<broadcast>", which specifies an INADDR_BROADCAST address.

· 

· 

A zero-length string, which specifies INADDR_ANY, or

· 

· 

An Integer, interpreted as a binary address in host byte order.

· 

5

port

Each server listens for clients calling on one or more ports. A port may be a Fixnum port number, a string comprising a port number, or the name of a service.

The socket Module

To make a socket, you must utilize the socket.socket() function easy to get to in socket module, which has the universal syntax:

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

Here is the description of the 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.

Once users possess socket object, in such scenarios, users could use the needed functions to create client or server program.

Following is the list of functions required –

Server Socket Methods

Sr.No.

Method & Description

1

s.bind()

This method binds address (hostname, port number pair) to socket.

2

s.listen()

This method sets up and start TCP listener.

3

s.accept()

This passively accept TCP client connection, waiting until connection arrives (blocking).

Client Socket Methods

Sr.No.

Method & Description

1

s.connect()

This method actively initiates TCP server connection.

General Socket Methods

Sr.No.

Method & Description

1

s.recv()

This method receives TCP message

2

s.send()

This method transmits TCP message

3

s.recvfrom()

This method receives UDP message

4

s.sendto()

This method transmits UDP message

5

s.close()

This method closes socket

6

socket.gethostname()

Returns the hostname.

A Simple Server

To write Internet servers, programmers need to utilize the socket function obtainable in socket module to develop a socket object. A socket object is then utilized to call additional functions to system a socket server.

Now call bind(hostname, port) function to state a port for service on the provided host.

Next, call the accept method of the returned object. This method stays unless a client attaches to the port that users specified, and then returns a connection object that depicts the link to that client.

#!/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

A Simple Client

Let us write a simple client program that unlocks a connection supposing to a provided port 54321 and host. This is simple to expand a socket user using Python's socket module function.

The socket.connect(hosname, port ) unbolts a TCP connection to hostname on the port. Once users possess a socket open, then they could interpret from accepting as IO object. When completed, keep in mind to close it, as users need to close a file.

The following code is a simple client that connects to a provided 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.

# Following would start a server in background.
$ python server.py & 

# Once server is started run client as follows:
$ python client.py

This would supply following result:

Got connection from ('127.0.0.1', 48437)
Thank you for connecting

Python Internet modules

A list of some important modules in Python Network/Internet programming.

Protocol

Common function

Port No

Python module

HTTP

Web pages

80

httplib, urllib, xmlrpclib

NNTP

Usenet news

119

Nntplib

FTP

File transfers

20

ftplib, urllib

SMTP

Sending email

25

Smtplib

POP3

Fetching email

110

Poplib

IMAP4

Fetching email

143

Imaplib

Telnet

Command lines

23

Telnetlib

Gopher

Document transfers

70

gopherlib, urllib

Please check all the libraries mentioned above to work with FTP, SMTP, POP, and IMAP protocols.

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