List attribute is shared amongst instances

Param
1

I have implemented a simulation where I observe the growth of a
recruiting network where the default strategy is:

each marketer recruits 1 person per month directly until they
reach 5 recruits, at which point, they no longer recruit any one.

The initial state of the simulation is 1 marketer with 0 recruits.

After 1 month, the 1 marketer recruits 1 person so the expected state
of the simulation is:

  • the first marketer has 1 recruit
  • the second marketer has 0 recruits

However, the output from my simulation shows the second marketer as
also having 1 recruit. But examining the output closer, the second
marketer has itself as a recruit. i.e, both the first marketer and the
second marketer have the second marketer as their first recruit:

c:\programming\mlm-sim>python mlm-sim.py 
python mlm-sim.py 
Month 0: Total marketers 1.
Marketer 1 has sponsored the following 0 marketers: []

	Recruiting complete. Updated status for month: Total marketers 2.
Marketer 1 has sponsored the following 1 marketers: [Marketer(front_line=[...], front_line_target=5, id=2, name='Marketer00004', sponsor=[])]
Marketer 2 has sponsored the following 1 marketers: [Marketer(front_line=[...], front_line_target=5, id=2, name='Marketer00004', sponsor=[])]

Month 1: Total marketers 2.
Marketer 1 has sponsored the following 1 marketers: [Marketer(front_line=[...], front_line_target=5, id=2, name='Marketer00004', sponsor=[])]
Marketer 2 has sponsored the following 1 marketers: [Marketer(front_line=[...], front_line_target=5, id=2, name='Marketer00004', sponsor=[])]

It seems that the front_line attribute that is added after the class
is defined is not unique amount Marketer instances for some reason
even though I used the instantiate=True keyword to enforce this.

Code follows:

import itertools

from param import Parameterized, Number, List, ClassSelector

marketer_id = itertools.count(1)


class Marketer(Parameterized):
    id = Number()
    front_line_target = Number(5)

    def __init__(self, **params):
        super().__init__(**params)
        self.id = next(marketer_id)

    @property
    def sponsoring_goals_met(self):
        return len(self.front_line) == self.front_line_target

    @classmethod
    def recruiting_strategy(cls):
        """Employ a strategy to recruit new marketers.

        Default algorithm recruits 1 new marketer.
        """
        new_marketer = Marketer()
        return [new_marketer]

    def recruit(self):
        if self.sponsoring_goals_met:
            return []
        else:
            new_marketers = self.recruiting_strategy()
            self.front_line.extend(new_marketers)
            return new_marketers

    def __str__(self):
        return f"Marketer {self.id} has sponsored the following {len(self.front_line)} marketers:\n\t{self.front_line}"


Marketer.param.add_parameter('sponsor', List([], item_type=Marketer, instantiate=True))
Marketer.param.add_parameter('front_line', List([], item_type=Marketer, instantiate=True))


class Network(Parameterized):
    marketers = List([], item_type=Marketer, instantiate=True)

    def recruit(self):
        new_marketers = []
        for marketer in self.marketers:
            new_marketers.extend(marketer.recruit())
        self.marketers.extend(new_marketers)

    def __str__(self):
        result = f"Total marketers {len(self.marketers)}.\n"
        for marketer in self.marketers:
            result = result + str(marketer) + "\n"
        return result


def main(months=3):
    network = Network()
    network.marketers.append(Marketer())

    for month in range(months):
        print(f"Month {month}: {network}")

        network.recruit()

        print(f"\tRecruiting complete. Updated status for month: {network}")


if __name__ == '__main__':
    main()
3

Yeah so maybe using add_parameter like that isn’t such a good idea, I can reproduce this issue with a simpler example:

image

Then you could use the approach suggested by @jbednar and update the class_ or item_type right after the class is created:

class Marketer(Parameterized):
    id = Number()
    front_line_target = Number(5)
    sponsor = List([], item_type=Parameterized, instantiate=True)
    front_line = List([], item_type=Parameterized, instantiate=True)

    def __init__(self, **params):
        super().__init__(**params)
        self.id = next(marketer_id)

    @property
    def sponsoring_goals_met(self):
        return len(self.front_line) == self.front_line_target

    @classmethod
    def recruiting_strategy(cls):
        """Employ a strategy to recruit new marketers.

        Default algorithm recruits 1 new marketer.
        """
        new_marketer = Marketer()
        return [new_marketer]

    def recruit(self):
        if self.sponsoring_goals_met:
            return []
        else:
            new_marketers = self.recruiting_strategy()
            self.front_line.extend(new_marketers)  # THIS IS WHERE SOMETHING WEIRD HAPPENS
            return new_marketers

    def __str__(self):
        return f"Marketer {self.id} has sponsored the following {len(self.front_line)} marketers:\n\t{self.front_line}"

Marketer.param.sponsor.item_type = Marketer
Marketer.param.front_line.item_type = Marketer