Question

Helo, I’m building a relatively complex Discrete Event Simulation Model in SimPy.

When I try to put my yield statements inside functions, my program doesn’t seem to work. Below shows an example.

import SimPy.SimulationTrace as Sim
import random

## Model components ##
class Customer(Sim.Process):
    def visit(self):
        yield Sim.hold, self, 2.0
        if random.random()<0.5:
            self.holdLong()
        else:
            self.holdShort()

    def holdLong(self):
        yield Sim.hold, self, 1.0
        # more yeild statements to follow

    def holdShort(self):
        yield Sim.hold, self, 0.5
        # more yeild statements to follow

## Experiment data ##
maxTime = 10.0 #minutes

## Model/Experiment ##
#random.seed(12345)
Sim.initialize()
c = Customer(name = "Klaus") #customer object
Sim.activate(c, c.visit(), at = 1.0)
Sim.simulate(until=maxTime)

The output I get from running this is:

0 activate <Klaus > at time: 1.0 prior: False
1.0 hold  < Klaus >  delay: 2.0
3.0 <Klaus > terminated

The holdLong() and holdShort methods didn’t seem to work at all. How can I fix this? Thanks in advance.

Answer 1

Calling a generator function returns a generator object that can be iterated over. You are simply ignoring this return value, so nothing happens. Instead, you should iterate over the generator and re-yield all values:

class Customer(Sim.Process):
    def visit(self):
        yield Sim.hold, self, 2.0
        if random.random()<0.5:
            for x in self.holdLong():
                yield x
        else:
            for x in self.holdShort():
                yield x