Compare value of property of all instances of class in python - class

Question

I'm trying to write an object oriented program (as a learning exercise, I know there may be simpler ways to do it) in which beads bounce around a 2D plane bounded by a ring. Each bead is an object defined by a class ball. In setting the initial positions of the balls I need to check that no other ball has already been placed at the same x and y coordinates.
#Class for the beads
class ball:
NumbBalls = 0
#Constructor
def __init__(self,Beads):
self.ball = sphere(pos = vector(0,0,0), radius = radiusBall,color=color.red)
ball.NumbBalls += 1
self.ball.pos = self.createInitialPosition(Beads)
#Assign ball its initial position
def createInitialPosition(self,other):
#CODE to compare self.ball.pos and other.ball.pos which returns a unique position coordinate
#Main program
NumbBeads = 100
Beads = []#Create empty list for all the beads
#create balls in random initial positions
Beads = [ball(Beads) for item in range(NumbBeads)]
I can get this to work if I create two objects bead1 and bead2 and then pass bead1 and bead2 as arguments ie bead2 = ball(bead1) but how do I do this if I am generating a list of beads and want all of them to be compared with self. Hopefully that makes sense.

Answer 1

Perhaps rather than the approach you are currently taking, you should consider something along these lines (of course, with the necessary changes to your class definition/methods):
N = 100
initialPositions = []
while len(initialPositions) <= N:
newPosition = generateRandomPosition()
if newPosition in initialPositions:
pass
else:
initialPositions.append(newPosition)
ballList = [ ball(p) for p in initialPositions ]
In other words, generate a list of initial positions outside of the creation of your objects, and do whatever validation/restriction you need during that creation. Then just create your objects from that list. If N is really large, you might want to consider a dictionary (or a mutable set of some sort) instead of a list for initialPositions, to help speed up the membership testing, but it's still the same concept...