OSError: [Errno 99] Cannot assign requested address - py

I just copied this code for a client/server example:

http://www.bogotobogo.com/python/python_network_programming_server_client.php

and when I run the code I get this error:

OSError: [Errno 99] Cannot assign requested address

Server:

# server.py 
import socket                                         
import time

# create a socket object
serversocket = socket.socket(
            socket.AF_INET, socket.SOCK_STREAM) 

# get local machine name
host = socket.gethostname()                           

port = 9999                                           

# bind to the port
serversocket.bind((host, port))                                  

# queue up to 5 requests
serversocket.listen(5)                                           

while True:
    # establish a connection
    clientsocket,addr = serversocket.accept()      

    print("Got a connection from %s" % str(addr))
    currentTime = time.ctime(time.time()) + "\r\n"
    clientsocket.send(currentTime.encode('ascii'))
    clientsocket.close()

Client:

# client.py  
import socket

# create a socket object
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 

# get local machine name
host = socket.gethostname()                           

port = 9999

# connection to hostname on the port.
s.connect((host, port))                               

# Receive no more than 1024 bytes
tm = s.recv(1024)                                     

s.close()

print("The time got from the server is %s" % tm.decode('ascii'))