Server File Transfer Using Python

import socket
import threading
import os

def RetrFile(name,sock):
print('control is before receiving the file name from client')
filename = sock.recv(1024).decode()
print('control is after receving the file name from client')
print('The file name received from the client is :'+filename)
if os.path.isfile(filename):
print('Inside the IF of server code')
msg = "EXISTS:"+str(os.path.getsize(filename))
print(msg)
sock.send(msg.encode())
userResponse = sock.recv(1024).decode()
print("The client responsed as :"+userResponse[:2])
if userResponse[:2] == 'OK':
with open(filename,'rb') as f:
bytesToSend = f.read(1024)
sock.send(bytesToSend)
while (bytesToSend):
bytesToSend = f.read(1024)
sock.send(bytesToSend)
else:
sock.send("ERROR".encode())

else:
sock.send("File Does not Exist".encode())
sock.close()

def Main():
host = socket.gethostname()
port = 5000

s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)#Creating the Server socket
s.bind((host,port)) #bind the host and port

s.listen(5)

print ('Server Started')
while True:
c,addr = s.accept()
print ('client connected ip:<'+str(addr)+'>')
#threading.Thread() method initiate a thread, the object is t
t = threading.Thread(target=RetrFile, args=('retrThread',c))
print('thread about to initiate')
#thread object.start() method starts the thread, execution of the thread starts
t.start()
s.close()

if __name__ == '__main__':
Main()