example_02.py

import math
import random

from datetime import datetime
random.seed(datetime.now().timestamp())

WORLD_WIDTH = 2560
WORLD_HEIGHT = 1440

class Agent():
    def __init__(self, x=None, y=None):
        super().__init__()

        # default values
        self.vmax = 2.0

        # initial position
        self.x = x if x else random.randint(0, WORLD_WIDTH)
        self.y = y if y else random.randint(0, WORLD_HEIGHT)

        # initial velocity
        self.dx = 0
        self.dy = 0

        # inital values
        self.is_alive = True
        self.target = None
        self.age = 0
        self.energy = 0

    def update(self, food=()):
        self.age = self.age + 1

        # we can't move
        if self.vmax == 0:
            return

        # target is dead, don't chase it further
        if self.target and not self.target.is_alive:
            self.target = None

        # eat the target if close enough
        if self.target:
            squared_dist = (self.x - self.target.x) ** 2 + (self.y - self.target.y) ** 2
            if squared_dist < 400:
                self.target.is_alive = False
                self.energy = self.energy + 1

        # agent doesn't have a target, find a new one
        if not self.target:
            min_dist = 9999999
            min_agent = None
            for a in food:
                if a is not self and a.is_alive:
                    sq_dist = (self.x - a.x) ** 2 + (self.y - a.y) ** 2
                    if sq_dist < min_dist:
                        min_dist = sq_dist
                        min_agent = a
            if min_dist < 100000:
                self.target = min_agent

        # initalize 'forces' to zero
        fx = 0
        fy = 0

        # move in the direction of the target, if any
        if self.target:
            fx += 0.1*(self.target.x - self.x)
            fy += 0.1*(self.target.y - self.y)

        # update our direction based on the 'force'
        self.dx = self.dx + 0.05 * fx
        self.dy = self.dy + 0.05 * fy

        # slow down agent if it moves faster than it max velocity
        velocity = math.sqrt(self.dx ** 2 + self.dy ** 2)
        if velocity > self.vmax:
            self.dx = (self.dx / velocity) * (self.vmax)
            self.dy = (self.dy / velocity) * (self.vmax)

        # update position based on delta x/y
        self.x = self.x + self.dx
        self.y = self.y + self.dy

        # ensure it stays within the world boundaries
        self.x = max(self.x, 0)
        self.x = min(self.x, WORLD_WIDTH)
        self.y = max(self.y, 0)
        self.y = min(self.y, WORLD_HEIGHT)

class Predator(Agent):
    def __init__(self, x=None, y=None):
        super().__init__()
        self.vmax = 2.5

class Prey(Agent):
    def __init__(self, x=None, y=None):
        super().__init__()
        self.vmax = 2.0

class Plant(Agent):
    def __init__(self, x=None, y=None):
        super().__init__()
        self.vmax = 0


def main():
    # open the ouput file
    f = open('output.csv', 'w')
    print(0, ',', 'Title', ',', 'Predator Prey Relationship / Example 02 / Pthon', file=f)

    # create initial agents
    preys = [Prey() for i in range(10)]
    predators = [Predator() for i in range(10)]
    plants = [Plant() for i in range(100)]

    timestep = 0
    while timestep < 10000:
        # update all agents
        #[f.update() for f in plants]  # no need to update the plants; they do not move
        [a.update(food=plants) for a in preys]
        [a.update(food=preys) for a in predators]

        # handle eaten and create new plant
        plants = [p for p in plants if p.is_alive is True]
        plants = plants + [Plant() for i in range(2)]

        # handle eaten and create new preys
        preys = [p for p in preys if p.is_alive is True]

        for p in preys[:]:
            if p.energy > 5:
                p.energy = 0
                preys.append(Prey(x = p.x + random.randint(-20, 20), y = p.y + random.randint(-20, 20)))

        # handle old and create new predators
        predators = [p for p in predators if p.age < 2000]

        for p in predators[:]:
            if p.energy > 10:
                p.energy = 0
                predators.append(Predator(x = p.x + random.randint(-20, 20), y = p.y + random.randint(-20, 20)))

        # write data to output file
        #[print(timestep, ',', 'Position', ',', 'Predator', ',', a.x, ',', a.y, file=f) for a in predators]
        #[print(timestep, ',', 'Position',  ',', 'Prey', ',', a.x, ',', a.y, file=f) for a in preys]
        #[print(timestep, ',', 'Position',  ',', 'Plant', ',', a.x, ',', a.y, file=f) for a in plants]

        timestep = timestep + 1

    print(len(predators), len(preys), len(plants))

if __name__ == "__main__":
    main()