We present Tython, a Python-based scripting extension to Tiny-OS's TOSSIM simulator. Tython includes a rich library of scripting primitives that enable users to describe dynamic but reproducible simulation scenarios. We take advantage of TinyOS's event driven execution to allow users to attach script callbacks to particular simulation scenarios. Scripts can also use interfaces at both a whole-network and a per-mote level to analyze and affect behavior in response to changes in the environment. We use the development of a Pursuer-Evader application as a running example to demonstrate the value of this approach.