Question

I’m using Python to make a simple evolution simulator.

There is a list called engine.All, that stores both the units/animals and food. I iterate through it, and if I run into an animal, I iterate through it once again to find if he is colliding with any of the food pieces.

If so, then I increase his energy, flag the food piece as eaten, and add it to the toRemove list, which I later use to remove the elements from engine.All.

This is the code, but with all redundant things removed:

def remove(l, who): #This should remove all the elements contained in who from the list l
    offset = 0

    for i in who:
        l.pop(i + offset)
        offset -= 1

    return l


for ob in engine.All:
    if ob.skip:
        continue;

    if ob.drawable:
       ob.draw()

    if isinstance(ob, Flatlander): #If it is an animal
        #Do speed stuff
        ob.energy -= decay #Lower its energy

        for i in range(len(engine.All)): #Iterate through the list again
            if collides(ob.pos, ob.r, engine.All[i].pos, engine.All[i].r) and isinstance(engine.All[i], Food) and ob.energy + engine.All[i].r < ob.r**2*3.14 and not engine.All[i].skip: #If it collides with a food piece, the food piece isn't about to be deleted and it can take the energy in (their maximum is defined by their radiuses)
                ob.energy += engine.All[i].r #Increase the his energy
                toRemove.append(i) #Add the food piece to the toRemove list
                engine.All[i].skip = True #Flag it as skipped

        if ob.energy < 0 and not ob.skip: #If its energy is 0 and if it isn't already about to be deleted
            toRemove.append(engine.All.index(ob)) #Add it to the toRemove list
            ob.skip = True #Flag it as skipped


engine.All = remove(engine.All, toRemove) 

I am almost certain that this doesn’t work, and that there is a better way of doing this. The reason I’m so certain is that sometimes, I see things just “flashing” on the screen – suddenly disappearing and appearing again. Also, there seem to be “ghost” animals (referred to as Flatlanders in the code), I conclude this because sometimes the food pieces are disappearing permanently.

Please, recommend a way of doing this that is more efficient.

Answer 1

If the skip attribute is only set for those objects which need to be removed, just make use of that:

import math
import itertools

for ob in engine.All:
    if isinstance(ob, Flatlander):
        ob.energy -= decay

for pair in itertools.combinations(engine.All, 2):
    fooditems = [x for x in pair if isinstance(x, Food) and not x.skip]
    animals = [x for x in pair if isinstance(x, Flatlander) and not x.skip]
    if not (fooditems and animals):
        continue
    animal = animals[0]
    food = fooditems[0]
    if collides(animal.pos, animal.r, food.pos, food.r):
        # This seems an odd calculation to me but I think it follows your code.
        if animal.energy + food.r < animal.r ** 2 * math.pi:
            # eating is feasible; the animal always eats the food if it can
            food.skip = True
            animal.energy += food.r # Not the area?

for ob in engine.All:
    if isinstance(ob, Flatlander) and ob.energy < 0:
        ob.skip = True # dead

# Remove dead things
engine.All = [ob for ob in engine.All if not ob.skip]

# Draw everything (no dead things remain)
for ob in engine.All:
    if ob.drawable:
      ob.draw()

Generally I would probably prefer to keep the food items and the flatlanders in separate lists.

There are several technique for doing collision detection more efficiently (for example dividing the world into squares, and checking only those animals in the same or surrounding squares) but if you have only a few (say less than a few hundred) animals/food items this will not be needed.