SimPy is an open-source, process-based discrete-event simulation language based on standard Python and released under the GNU GPL. It provides the modeller with components of a simulation model including processes, for active components like customers, messages, and vehicles, and resources, for passive components that form limited capacity congestion points like servers, checkout counters, and tunnels. It also provides monitor variables to aid in gathering statistics. Random variates are provided by the standard Python random module.

Simpy is based on ideas from Simula and SIMSCRIPT II.5 but uses standard Python. It combines two previous packages, SiPy, in Simula-Style and SimPy, in Simscript style.

SimPy uses an efficient implementation of co-routines using Python's generators capability. It requires Python 2.2 or later.

More information can be obtained from the Simpy page on Sourceforge.