Messages are the units processed by the resources and can store arbitrary information, called properties in SimPype. Message properties can be of any values, including Random objects (see Random variables). See Message for a detailed API reference.

import simpype
import random

sim = simpype.Simulation(id = 'simple')
gen0 = sim.add_generator(id = 'gen0')['rand_prop'] = {
    # Every message generated between t=0 and t=10 will have
    # the 'test' property value equal to 3.0
    0 : lambda: 3.0,
    # Every message generated between t=10 and t=20 will have
    # the 'test' property uniformly distributed between 2.5 and 3.5
    10: lambda: random.uniform(2.5, 3.5),
    # Every message generated between t=20 and t=inf will have
    # the 'test' property exponentially distributed with lambda 0.20
    20: lambda: random.expovariate(0.20)
# Store the property as normal dictionary if no lambda functions is present['dict_prop'] = {
    'a': 'avalue',
    'b': 'bvalue',
}['str_prop'] = 'mystr'['int_prop'] = 3['float_prop'] = 3.0
# You can also store objects
e = sim.env.event()['event_prop'] = e

Please note that in this case there is no need of calling the simpype.Random constructor. The message object automatically converts the dictionary into a Random object. Please also note that property values can be randomly generated, nevertheless once they are generated they will always return the same value unless an explicit refresh is called['test'].refresh()


A message can be suddenly dropped by calling the function drop():

message.drop(id = 'bad luck')

In addition, a message can be dropped upon the occurence of a given event:

# Create a SimPy event
e = sim.env.event()
# Subscribe the dropping of the message to the event e
message.drop(id = 'event bad luck', event = e)
# Trigger the event
# The message has now been dropped

The message is dropped only when the event e is triggered, that is succeed in SimPy notation.


A lifetime can be assigned to generated messages in the following way:

import simpype
import random

sim = simpype.Simulation(id = 'simple')
gen0 = sim.add_generator(id = 'gen0')['lifetime'] = {
    0: lambda: random.expovariate(0.20)

The message is dropped when the lifetime expires. To remove any lifetime from the message, use the following function:

message.unsubscribe(id = 'lifetime')

Event subscription

A message can be susbscribed to a given event and a custom function can be executed upong event triggering, e.g.:

import simpype
import random

sim = simpype.Simulation(id = 'simple')
gen0 = sim.add_generator(id = 'gen0')
res0 = sim.add_resource(id = 'res0')
res1 = sim.add_resource(id = 'res1')

e = sim.env.event()
def c(message, value):
    # Value of the event, e.g. 'OK'['myevent'] = value

def service(self, message):
    global e
    # Trigger the event
    e.succeed(value = 'OK')
    e = sim.env.event()

def service(self, message):
    # Unsubscribe from the event
    message.unsubscribe(id = 'mysub')

gen0.message.subscribe(event = e, callback = c, id = 'mysub')

The callback function must be defined according to the following format:

def callback(message, value):
    ... your code here ...