Check out example codes for "simpy process return value". It will help you in understanding the concepts better.

Code Example 1

import simpy

def example(env):
     value = yield env.timeout(1, value=42)
     print('now=%d, value=%d' % (env.now, value))

env = simpy.Environment()
p = env.process(example(env))
env.run()
#now=1, value=42

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