ns-3 can be used to quickly prototype network protocol implementations and applications. Once you have configured ns-3 correctly, you may start running the Python examples from the folder ns-allinone-3.26/ns-3.26/examples/tutorial. More information on this can be found from https://www.nsnam.org/docs/manual/html/python.html.

Listing 9.1 simulates a network with two nodes with UDP messages between them:

#!/usr/bin/env python 
# Python Network Programming Cookbook, Second Edition -- Chapter - 9 
# This program is optimized for Python 2.7.12 and Python 3.5.2. 
# It may run on any other version with/without modifications. 
 
import ns.applications 
import ns.core 
import ns.internet 
import ns.network 
import ns.point_to_point 
import argparse 
 
 
def simulate(ipv4add, ipv4mask): 
    # Enabling logs at INFO level for both the server and the client. 
    ns.core.LogComponentEnable("UdpEchoClientApplication",
     ns.core.LOG_LEVEL_INFO) 
    ns.core.LogComponentEnable("UdpEchoServerApplication",
     ns.core.LOG_LEVEL_INFO) 
     
    # Create the 2 nodes. 
    nodes = ns.network.NodeContainer() 
    nodes.Create(2) 
 
    pointToPoint = ns.point_to_point.PointToPointHelper() 
 
    devices = pointToPoint.Install(nodes) 
 
    stack = ns.internet.InternetStackHelper() 
    stack.Install(nodes) 
 
    # Set addresses based on the input args. 
    address = ns.internet.Ipv4AddressHelper() 
    address.SetBase(ns.network.Ipv4Address(ipv4add),
     ns.network.Ipv4Mask(ipv4mask)) 
 
    interfaces = address.Assign(devices) 
 
    # Running the echo server 
    echoServer = ns.applications.UdpEchoServerHelper(9) 
    serverApps = echoServer.Install(nodes.Get(1)) 
 
    # Running the echo client 
    echoClient = ns.applications.
    UdpEchoClientHelper(interfaces.GetAddress(1), 3) 
    clientApps = echoClient.Install(nodes.Get(0)) 
 
    # Running the simulator 
    ns.core.Simulator.Run() 
    ns.core.Simulator.Destroy() 
 
 
if __name__ == '__main__': 
    parser = argparse.ArgumentParser(description='NS-3 Simple Simulation') 
    parser.add_argument('--ipv4add', action="store",
     dest="ipv4add", type=str, required=True) 
    parser.add_argument('--ipv4mask', action="store",
     dest="ipv4mask", type=str, required=True) 
    given_args = parser.parse_args() 
    simulate(given_args.ipv4add, given_args.ipv4mask) 

First run the waf shell to get the dependencies for the ns-3 simulation before executing the actual simulation:

ns-allinone-3.26/ns-3.26$ ./waf shell  

Next, run the simulation:

python 9_1_ns3_simulation.py --ipv4add=100.10.100.0 --ipv4mask=255.255.255.0
At time 0s client sent 100 bytes to 100.10.100.2 port 3
At time 1s client sent 100 bytes to 100.10.100.2 port 3
At time 2s client sent 100 bytes to 100.10.100.2 port 3
...
At time 97s client sent 100 bytes to 100.10.100.2 port 3
At time 98s client sent 100 bytes to 100.10.100.2 port 3
At time 99s client sent 100 bytes to 100.10.100.2 port 3