Python is a widely used general purpose programming language. It is a great first language for teaching purposes, and also a language that is in high demand in industry. Even better, it is free and open source, installed by default on most Linux and Mac OSX systems, and easily installed on Windows.
Mininet is a Linux-based network emulator which enables the creation of a realistic virtual network, running real kernel, switch and application code, on a single machine (VM, cloud or native), in seconds, with a single command. It is a great way to develop, share, prototype, research, teach and experiment with OpenFlow and Software-Defined Networking systems.