Running a Simpy simulation until a given value

Question

I'm new to SymPy (3.0.8) and would like to run a demo simulation 'conference attendee' until a give value (250), i.e. run until talk 7 (3 talks, 1 break, 3 talks, 1 break, 1 talk).

3*30 + 15 + 3*30 + 15 + 1*30 = 240

But the simulation ends after 3 talks, 1 break, 3 talks and 1 break (210).

I'd like to know why the simulations does not run until 'talk 7' and how to fix this.

# import
import simpy
from random import randint

# config
TALKS_PER_SESSION = 3
TALK_LENGTH = 30
BREAK_LENGTH = 15
ATTENDEES = 3

# process function
def attendee(env, name, knowledge=0, hunger=0):
    talks = 0
    breaks = 0
    while True:
        # Visit talks
        for i in range(TALKS_PER_SESSION):
            knowledge += randint(0, 3) / (1 + hunger)
            hunger += randint(1, 4)
            talks += 1
            yield env.timeout(TALK_LENGTH)

        print('Attendee %s finished %d talks with knowledge %.2f and hunger %.2f.' % (name, talks, knowledge, hunger))

        # Go to buffet
        food = randint(3, 12)
        hunger -= min(food, hunger)
        breaks += 1

        yield env.timeout(BREAK_LENGTH)

        print('Attendee %s has finished break %d with hunger %.2f' % (name, breaks, hunger))

# setup environment and run simulation
env = simpy.Environment()
for i in range(ATTENDEES):
    env.process(attendee(env, i))
env.run(until=250)

The output of this simulation is:

Attendee 0 finished 3 talks with knowledge 2.33 and hunger 7.00.
Attendee 1 finished 3 talks with knowledge 0.60 and hunger 8.00.
Attendee 2 finished 3 talks with knowledge 3.81 and hunger 7.00.
Attendee 0 has finished break 1 with hunger 0.00
Attendee 1 has finished break 1 with hunger 0.00
Attendee 2 has finished break 1 with hunger 0.00
Attendee 0 finished 6 talks with knowledge 5.53 and hunger 6.00.
Attendee 1 finished 6 talks with knowledge 1.89 and hunger 9.00.
Attendee 2 finished 6 talks with knowledge 4.31 and hunger 5.00.
Attendee 0 has finished break 2 with hunger 0.00
Attendee 1 has finished break 2 with hunger 0.00
Attendee 2 has finished break 2 with hunger 0.00

But I expected it to be:

Attendee 0 finished 3 talks with knowledge 2.33 and hunger 7.00.
Attendee 1 finished 3 talks with knowledge 0.60 and hunger 8.00.
Attendee 2 finished 3 talks with knowledge 3.81 and hunger 7.00.
Attendee 0 has finished break 1 with hunger 0.00
Attendee 1 has finished break 1 with hunger 0.00
Attendee 2 has finished break 1 with hunger 0.00
Attendee 0 finished 6 talks with knowledge 5.53 and hunger 6.00.
Attendee 1 finished 6 talks with knowledge 1.89 and hunger 9.00.
Attendee 2 finished 6 talks with knowledge 4.31 and hunger 5.00.
Attendee 0 has finished break 2 with hunger 0.00
Attendee 1 has finished break 2 with hunger 0.00
Attendee 2 has finished break 2 with hunger 0.00
Attendee 0 finished 7 talks with knowledge <...> and hunger <...>.
Attendee 1 finished 7 talks with knowledge <...> and hunger <...>.
Attendee 2 finished 7 talks with knowledge <...> and hunger <...>.

Answer 1

Please set ATTENDEES = 1 and change the inner for loop to:

    for i in range(TALKS_PER_SESSION):
        print(f'Talk {talks+1} begins at {env.now}')
        knowledge += randint(0, 3) / (1 + hunger)
        hunger += randint(1, 4)
        talks += 1
        yield env.timeout(TALK_LENGTH)
        print(f'Talk {talks} ends at {env.now}')

When you let your simulation run again and think about what happens, you should understand that the output you get is correct. :)