Particle System V2

import pygame,sys
from pygame.locals import *
from pygame import gfxdraw
from random import randint
import math
pygame.init()

options = input("Default Settings> (y/n):")

class wld():
    def __init__(self,options):
        self.clock = pygame.time.Clock()
        self.FPS = 60
        self.bls = []
        if options == "n":
            self.x = int(input("X Resolution:"))
            self.y = int(input("Y Resolution:"))
            self.g = float(input("Acceleration due to gravity:"))
            self.r = int(input("Particle radius:"))
            self.c = input("Colour according to rms or component velocity? (rms/com):")
            self.f = abs(int(input("Drag (Higher = Less Drag):")))
        else:
            self.x,self.y,self.g,self.r,self.f,self.c = 500,500,9.81,4,500,"rms"
        self.num = int(input("How Many Balls? (0 for random):"))
        if (self.num == 0):
            self.num = randint(1,1000)
        if self.f <= 1 and self.f >=0:
            self.f = 1
        self.screen = pygame.display.set_mode((self.x,self.y))


class Balls():
    def __init__(self):
        self.radius = world.r
        self.ydisplacement = (world.y/2)
        self.xdisplacement = (world.x/2)
        self.yvelocity = randint(int(-world.y/3),int(world.y/3))
        self.xvelocity = randint(int(-world.x/3),int(world.x/3))
        self.xlist = []
        self.ylist = []
        self.time = 0
        self.falltime = 0
        self.bouncetime = 0

    def get_motion(self):
        self.time = self.time + 0.001
        self.falltime = self.falltime + 0.001
        self.bouncetime = self.bouncetime + 0.001
        self.yvelocity = self.yvelocity + 2 * world.g * self.falltime
        self.ydisplacement = self.ydisplacement + self.yvelocity * self.falltime + 0.5 * world.g * self.falltime
        self.xdisplacement = self.xdisplacement + self.xvelocity * self.bouncetime

    def friction(self):
        if not self.xvelocity == 0 and self.xvelocity >= 0:
            self.xvelocity = self.xvelocity - self.xvelocity/world.f
        elif not self.xvelocity == 0 and self.xvelocity <= 0:
            self.xvelocity = self.xvelocity - self.xvelocity/world.f
        if self.xvelocity >= -0.2 and self.xvelocity <= 0.2:
            self.xvelocity = 0

    def calc_ybounce(self):
        if self.ydisplacement >= world.y - self.radius:
            self.yvelocity = (-1) * self.yvelocity
            self.ydisplacement = world.y - self.radius
            self.bouncetime = 0

        if self.ydisplacement <= 0+self.radius:
            self.yvelocity = (-1) * self.yvelocity
            self.ydisplacement = 0+self.radius
            self.bouncetime =0

    def calc_xbounce(self):
        if self.xdisplacement >= world.x - self.radius:
            self.xvelocity = (-1) * self.xvelocity
            self.xdisplacement = world.x - self.radius

        if self.xdisplacement <= 0 + self.radius:
            self.xvelocity = (-1) * self.xvelocity
            self.xdisplacement = 0 + self.radius

    def draw(self):
        self.col = int((((self.xvelocity**2)+(self.yvelocity**2))/2)**0.5)
        if world.c == "com":
            pygame.gfxdraw.filled_circle(world.screen,int(self.xdisplacement),int(self.ydisplacement),self.radius,(self.col/2,abs(int(self.yvelocity)),abs(int(self.xvelocity))))
            pygame.gfxdraw.aacircle(world.screen,int(self.xdisplacement),int(self.ydisplacement),self.radius,(self.col/2,abs(int(self.yvelocity)),abs(int(self.xvelocity))))
        else:
            pygame.gfxdraw.filled_circle(world.screen,int(self.xdisplacement),int(self.ydisplacement),self.radius,(50,self.col,self.col/2))
            pygame.gfxdraw.aacircle(world.screen,int(self.xdisplacement),int(self.ydisplacement),self.radius,(50,self.col,self.col/2))

    def tick(self):
        self.get_motion()
        self.friction()
        self.calc_ybounce()
        self.calc_xbounce()
        self.draw()

world = wld(options)
for i in range(0,world.num):
    world.bls.append(Balls())

while True:
    world.screen.fill((200,200,200))
    tick = world.clock.tick(world.FPS)
    for i in range(0,world.num):
        world.bls[i].tick()
    pygame.display.update()

    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()
        if event.type == pygame.KEYDOWN and event.key == pygame.K_SPACE and len(world.bls) <= 500:
            if world.graphing:
                world.graphing = False
            else:
                world.graphing = True