Deleting/Duplicating an instance of a class when there are many

I am trying to delete the dots outside of the safe zone but so far the only solution I have found is to not draw them, which is not what I want since using this method they still exist. Is there anyway to delete the specific dots outside of this region? Is there also a way to create a duplicate of an instance?

import pygame
import sys
import random
pygame.init()
win = pygame.display.set_mode((800,600))
pygame.display.set_caption("Simulation")

class Dot:
    def __init__(self):
        self.spawnX = random.randrange(0, 800)
        self.spawnY = random.randrange(0, 600)
        self.r = random.randrange(0, 256)
        self.g = random.randrange(0, 256)
        self.b = random.randrange(0, 256)

        self.vel = [None] * 0
        self.spd = random.random()
        self.vel.append(self.spd)
        self.vel.append(self.spd * -1)
        self.fertility = random.randrange(0, 3)

def safeZone():
        #Draws a top rectangle
    pygame.draw.rect(win, (50,205,50), (0, 0, 800, 100))
        
def drawdot(dot):
    width = 10
    height = 10
    pygame.draw.rect(win, (dot.r, dot.g, dot.b), (dot.spawnX, dot.spawnY, width, height))

def population(dots):
    for dot in dots:
        dot.spawnX += random.choice(dot.vel)
        dot.spawnY += random.choice(dot.vel)
        if dot.spawnX >= 800:
            dot.spawnX -= 5
        if dot.spawnY >= 600:
            dot.spawnY -= 5
        if dot.spawnX <= 0:
            dot.spawnX += 5
        if dot.spawnY <= 0:
            dot.spawnY += 5
        if dot.spawnX >= 0 and dot.spawnY >= 100:
            pass  #Here I want to delete the objects outside of this region
        drawdot(dot)

alldots = [Dot() for _ in range(1000)]

run = True
while run:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
    win.fill((255, 255, 255))
    safeZone() # Always draw dots after safe zone
    population(alldots)
    pygame.display.update()

>Solution :

"not draw them" just means removing them from the container they are in. Use pygame.Rect.colliderect or pygame.Rect.contains to test whether a dot object is in the safe zone. Remove the dots form the list alldots that are not in the safe zone (see How to remove items from a list while iterating?):

def population(dots):

    safe_zone_rect = pygame.Rect(0, 0, 800, 100)
    
    for dot in dots:
        dot.spawnX += random.choice(dot.vel)
        dot.spawnY += random.choice(dot.vel)
        if dot.spawnX >= 800:
            dot.spawnX -= 5
        if dot.spawnY >= 600:
            dot.spawnY -= 5
        if dot.spawnX <= 0:
            dot.spawnX += 5
        if dot.spawnY <= 0:
            dot.spawnY += 5
        if dot.spawnX >= 0 and dot.spawnY >= 100:
            pass  #Here I want to delete the objects outside of this region

        dot_rect = pygame.Rect(dot.spawnX, dot.spawnY, 10, 10)
        # if not safe_zone_rect.colliderect(dot_rect):
        if not safe_zone_rect.contains(dot_rect):
            dots.remove(dot)

        drawdot(dot)

pygame.Rect.colliderect tests whether 2 rectangles intersect. pygame.Rect.contains
tests whether a rectangle lies completely within another rectangle.