Sockets | Python

What is socket?
Sockets act as bidirectional communications channel where they are endpoints of it.sockets may communicate within the process, between different process and also process on different places.
Socket Module- s.socket.socket(socket_family, socket_type, protocol=0)

• socket_family-AF_UNIX or AF_INET
• socket_type-SOCK_STREAM or SOCK_DGRAM
• protocol-left out, ot defaulting to 0

Once socket object is created as mentioned above, now we can use functions below to create client server programs. 
Socket methods

Sr no.	Method and Description
Server socket methods
1.	s.bind – This method binds address hostname, port number to socket
2.	s.listen – This method setups and start TCP listener
3.	s.accept – This passively accepts client connection, waiting until connection arrives blocking
Client socket methods
1.	s.connect – This method actively initiates TCP server connection

General socket methods

Sr no.	Method and 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.	s.gethostname – Returns a hostname

Examples: sending date from server to client

client side
Output :today's Date

Python3

# importing required modules
import socket
import datetime

# initializing socket
s = socket.socket()
host = socket.gethostname()
port = 12345

# binding port and host
s.bind((host, port))

# waiting for a client to connect
s.listen(5)

while True:
   # accept connection
   c, addr = s.accept()
   print ('got connection from addr', addr)
   date = datetime.datetime.now()
   d = str(date)

   # sending data type should be string and encode before sending
   c.send(d.encode())
   c.close()

Python3

import socket
s = socket.socket()
host = socket.gethostname()
port = 12345

# connect to host
s.connect((host, port))

# recv message and decode here 1024 is buffer size.
print (s.recv(1024).decode())
s.close()

Note: Create 2 instances of python compiler to run client and server code separately do not run them on the same instance.
Output:
Server side-

Client side-
Here current date time which is fetched from server appears 

UDP Sockets

UDP is USER DATAGRAM PROTOCOL, this is a lightweight protocol which has basic error checking mechanism with no acknowledgement and no sequencing but very fast due to these reasons
Examples:sending date from server to client

client side
Input : vivek  
Input : 17BIT0382  
Output : password match 

Python3

import socket

localIP = "127.0.0.1"
localPort = 20001
bufferSize = 1024

UDPServerSocket = socket.socket(family = socket.AF_INET, type = socket.SOCK_DGRAM)
UDPServerSocket.bind((localIP, localPort))
print("UDP server up and listening")

# this might be database or a file
di ={'17BIT0382':'vivek', '17BEC0647':'shikhar', '17BEC0150':'tanveer',
'17BCE2119':'sahil', '17BIT0123':'sidhant'}

while(True):
   # receiving name from client
   name, addr1 = UDPServerSocket.recvfrom(bufferSize)

   # receiving pwd from client
   pwd, addr1 = UDPServerSocket.recvfrom(bufferSize)

   name = name.decode()
   pwd = pwd.decode()
   msg =''
   if name not in di:
       msg ='name does not exists'
       flag = 0
   for i in di:
      if i == name:
          if di[i]== pwd:
              msg ="pwd match"
              flag = 1
          else:
              msg ="pwd wrong"
      bytesToSend = str.encode(msg)
      # sending encoded status of name and pwd
      UDPServerSocket.sendto(bytesToSend, addr1)

Python3

import socket

# user input
name = input('enter your username : ')
bytesToSend1 = str.encode(name)
password = input('enter your password : ')
bytesToSend2 = str.encode(password)

serverAddrPort = ("127.0.0.1", 20001)
bufferSize = 1024

# connecting to hosts
UDPClientSocket = socket.socket(family = socket.AF_INET, type = socket.SOCK_DGRAM)

# sending username by encoding it
UDPClientSocket.sendto(bytesToSend1, serverAddrPort)
# sending password by encoding it
UDPClientSocket.sendto(bytesToSend2, serverAddrPort)

# receiving status from server
msgFromServer = UDPClientSocket.recvfrom(bufferSize)
msg = "Message from Server {}".format(msgFromServer[0].decode())
print(msg)

For simplicity in the code, I have chosen a dictionary you can use a database, file or CSV file, etc. for various other purposes. 
Output: