Note: Simpy 3 is currently in development. Everything we promise below may or may not yet exist, may dramatically change or even explode! Nevertheless, we encourage you to try out the development version and tell us what you think.

SimPy is a process-based discrete-event simulation framework based on standard Python. Its event dispatcher is based on Python’s generators and can also be used for asynchronous networking or to implement multi-agent systems (with both, simulated and real communication).

Processes in SimPy are simple Python generator functions and are used to model active components like customers, vehicles or agents. SimPy also provides various types of shared resource to model limited capacity congestion points (like servers, checkout counters and tunnels). It will also provides monitoring capabilities to aid in gathering statistics about resources and processes.

Simulations can be performed “as fast as possible”, in real time (wall clock time) or by manually stepping through the events.

The distribution contains in-depth documentation, tutorials, and a large number of examples.

Simpy is released under the GNU LGPL. Simulation model developers are encouraged to share their SimPy modeling techniques with the SimPy community. Please post a message to the SimPy-Users mailing list.

A Simple Example

One of SimPy's main goals is to be easy to use. Here is an example for a simple SimPy simulation: a clock process that prints the current simulation time at each step:

>>> import simpy
>>> def clock(env):
...     while True:
...         print(
...         yield env.timeout(1)
>>> env = simpy.Environment()
>>> env.start(clock(env))
>>> simpy.simulate(env, until=3)


SimPy requires Python 2.7, 3.2, PyPy 2.0 or above.

You can install SimPy easily via PIP:

$ pip install -U SimPy

You can also download and install SimPy manually:

$ cd where/you/put/simpy/
$ python install

To run SimPy’s test suite on your installation, execute:

$ python -c "import simpy; simpy.test()"

Getting started

If you’ve never used SimPy before, the SimPy tutorial is a good starting point for you. You can also try out some of the Examples shipped with SimPy.

Documentation and Help

In our online documentation, you can find a tutorial, examples, topical guides and an API reference, as well as some information about SimPy and its history. For more help, contact the SimPy-Users mailing list. SimPy users are pretty helpful.

If you find any bugs, please post them on our issue tracker.

Enjoy simulation programming in SimPy!