Socket Programming with Multi-threading in Python

Prerequisite : Socket Programming in Python, Multi-threading in Python
Socket Programming-> It helps us to connect a client to a server. Client is message sender and receiver and server is just a listener that works on data sent by client.
What is a Thread? 
A thread is a light-weight process that does not require much memory overhead, they are cheaper than processes.
What is Multi-threading Socket Programming? port on your computer
Multithreading is a process of executing multiple threads simultaneously in a single process.
Multi-threading Modules : 
A _thread module & threading module is used for multi-threading in python, these modules help in synchronization and provide a lock to a thread in use. 
 

from _thread import *
import threading

A lock object is created by-> 
 

print_lock = threading.Lock()

A lock has two states, "locked" or "unlocked". It has two basic methods acquire() and release(). When the state is unlocked print_lock.acquire() is used to change state to locked and print_lock.release() is used to change state to unlock.
The function thread.start_new_thread() is used to start a new thread and return its identifier. The first argument is the function to call and its second argument is a tuple containing the positional list of arguments.
Let's study client-server multithreading socket programming by code- 
Note:-The code works with python3. 
Multi-threaded Server Code 
 

# import socket programming library
import socket

# import thread module
from _thread import *
import threading

print_lock = threading.Lock()

# thread function
def threaded(c):
    while True:

        # data received from client
        data = c.recv(1024)
        if not data:
            print('Bye')
            
            # lock released on exit
            print_lock.release()
            break

        # reverse the given string from client
        data = data[::-1]

        # send back reversed string to client
        c.send(data)

    # connection closed
    c.close()


def Main():
    host = ""

    # reserve a port on your computer
    # in our case it is 12345 but it
    # can be anything
    port = 12345
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.bind((host, port))
    print("socket binded to port", port)

    # put the socket into listening mode
    s.listen(5)
    print("socket is listening")

    # a forever loop until client wants to exit
    while True:

        # establish connection with client
        c, addr = s.accept()

        # lock acquired by client
        print_lock.acquire()
        print('Connected to :', addr[0], ':', addr[1])

        # Start a new thread and return its identifier
        start_new_thread(threaded, (c,))
    s.close()


if __name__ == '__main__':
    Main()

Console Window:
socket binded to port 12345
socket is listening
Connected to : 127.0.0.1 : 11600
Bye

Client Code 
 

# Import socket module
import socket


def Main():
    # local host IP '127.0.0.1'
    host = '127.0.0.1'

    # Define the port on which you want to connect
    port = 12345

    s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)

    # connect to server on local computer
    s.connect((host,port))

    # message you send to server
    message = "shaurya says geeksforgeeks"
    while True:

        # message sent to server
        s.send(message.encode('ascii'))

        # message received from server
        data = s.recv(1024)

        # print the received message
        # here it would be a reverse of sent message
        print('Received from the server :',str(data.decode('ascii')))

        # ask the client whether he wants to continue
        ans = input('\nDo you want to continue(y/n) :')
        if ans == 'y':
            continue
        else:
            break
    # close the connection
    s.close()

if __name__ == '__main__':
    Main()

Console Window:
Received from the server : skeegrofskeeg syas ayruahs

Do you want to continue(y/n) :y
Received from the server : skeegrofskeeg syas ayruahs

Do you want to continue(y/n) :n

Process finished with exit code 0

Reference-> 
https://docs.python.org/2/library/thread.html