Life and death model in python

Question

The basic idea of the code is that agents come into the world, they age and then die. I want to keep track of who is dead and who is alive. Eventually, they will do more things but I think there should be a lot of things I am not doing best practice on. I assume I'm doing something wrong with "Global" as well.

# Classes

class Agent(object):
    def __init__(self, identification, productivity, wealth, preferences, age, health, alive, sex):
        self.identification = identification
        self.productivity = productivity
        self.wealth = wealth
        self.preferences = preferences
        self.age = age
        self.health = health
        self.alive = alive
        self.sex = sex
    def description(self):
        print("My id is", self.identification)
        print("My age is", self.age)

def Create_agents():
    global id
    alive.append(Agent(id,100,20,"blue",30,0,True,True ))
    id += 1

# functions
def Initialize():
    for x in range(3):
        Create_agents()

def Death():
    temp = alive.copy()
    for agent in temp:
        if agent.age>30:
            agent.alive = False
            print("Death of", agent.identification)
            dead.append(agent)
            alive.remove(agent)

def Time_skip():
    print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%SKIPPING TIME%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
    global year
    year += 1
    print("The new year is", year)
    for agent in alive:
        agent.age +=1
    Create_agents()
    Death()


# Values
alive = []
dead = []
id = 0
year = 0
Initialize()

# Testing
for agent in alive: 
    agent.description()

Time_skip()

for agent in alive: 
    agent.description()

The output is:

My id is 0
My age is 30
My id is 1
My age is 30
My id is 2
My age is 30
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%SKIPPING TIME%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
The new year is 1
Death of 0
Death of 1
Death of 2
My id is 3
My age is 30

Answer 1

• Python has a standardized style guide called PEP 8. There is also Google's Python style guide which AFAIK is very similar to PEP 8.

  Any code that goes largely against PEP 8 normally doesn't look Pythonic.

  • Python has a naming scheme to allow developers to know the variables type by it's name only.

    • Classes are in CamelCase,
    • Functions, methods and variables are in snake_case, and
    • Constants are in UPPER_SNAKE_CASE.

  • There should be a single space after commas.

  • Lines should be limited to 79 characters.
  • There should be one space between all methods, and two between top level classes and functions.

  Overall your code adheres to these standards pretty well. Good job.

• class Agent(object) is a relic from Python 2. In Python 2 classes didn't inherit from object by default. These are now called old style classes. However in Python 3 everything inherits from object by default - making all classes in Python 3 new style classes.

• Your code would benefit from another class.

  I'm reluctant to suggest this as the code has an over-reliance on global variables. In the future you should try to solve the problem without globals and then see if it can be made cleaner by using a class.

  And so we can make a Simulation class. I would include all the global functions you have in it except initialize.

• I would use an if __name__ == "__main__": guard to prevent your code from running if it's been imported accidentally.

This gets the following. There's some more changes that can be made, but the base of your code is good.

class Agent:
    def __init__(self, identification, productivity, wealth, preferences, age, health, alive, sex):
        self.identification = identification
        self.productivity = productivity
        self.wealth = wealth
        self.preferences = preferences
        self.age = age
        self.health = health
        self.alive = alive
        self.sex = sex

    def description(self):
        print("My id is", self.identification)
        print("My age is", self.age)


class Simulation:
    def __init__(self):
        self.alive = []
        self.dead = []
        self._id = 0
        self.year = 0

    def create_agent(self):
        self.alive.append(Agent(self._id, 100, 20, "blue", 30, 0, True, True))
        self._id += 1

    def deaths(self):
        for agent in self.alive.copy():
            if agent.age > 30:
                agent.alive = False
                print("Death of", agent.identification)
                self.dead.append(agent)
                self.alive.remove(agent)

    def time_skip(self):
        print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%SKIPPING TIME%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
        self.year += 1
        print("The new year is", self.year)
        for agent in self.alive:
            agent.age += 1
        self.create_agent()
        self.deaths()

if __name__ == '__main__':
    simulation = Simulation()
    for _ in range(3):
        simulation.create_agent()

    # Testing
    for agent in simulation.alive: 
        agent.description()

    simulation.time_skip()

    for agent in simulation.alive: 
        agent.description()

Answer 2

Instead of using either global variables or another class to manage the collections of agents, you could use class variables that do that for you. Consider this (reduced) example of an Agent class:

class Agent:
    id_ = 0
    alive = set()
    dead = set()

    def __init__(self):
        self.id = Agent.id_
        Agent.id_ += 1
        self.alive = True
        Agent.alive.add(self)

    def die(self):
        self.alive = False
        Agent.alive.remove(self)
        Agent.dead.add(self)

    def __repr__(self):
        return f"Agent(id={self.id})"

which you can use like this:

agents = [Agent() for _ in range(3)]
print(Agent.alive)
# {Agent(id=1), Agent(id=0), Agent(id=2)}
agents[1].die()
print(Agent.alive)
# {Agent(id=0), Agent(id=2)}
print(Agent.dead)
# {Agent(id=1)}

Apart from that I agree with all the other points in the excellent answer by @Peilonrayz.