Pull and release ball 2

from random import randint, uniform
import time, sys
import pygame
from pygame import Rect as R
from pygame import Vector2 as V
from pygame.locals import *

class particle:
    def __init__(s, xy, vel): # xy = tuple(x, y)
        # position of the particle
        s.xy = V(xy)

        # particle velocity
        s.vel = vel #Vector2(uniform(-1, 1), uniform(-4.5, -5)) # x vel is betweem -1 & 1 and y vel is between -4.5 and -5

        # particle radius
        s.radius = randint(20, 30) # random integer between 5 & 15

    # draw particle and update position/size
    def update(s):
        global dt
        global GRAVITY
        global PDS, WHITE # PDS = primary display surface

        # draw particle
        pygame.draw.circle(PDS, (128, 128, 128), s.xy, s.radius)

        # draw glow
        s.glow()

        # add velocity to particle
        s.xy += s.vel * dt

        # add gravity to velocity. negative velocity will slowly become positive
        s.vel.y += GRAVITY * dt

        # decrease radius to give a fizzling out effect
        s.radius -= 0.1 * dt

    def glow(s):
        global PDS
        # get rectangular size of the particle. radius * 2
        r = V(s.radius) * 2 # r = (radius * 2, radius * 2)

        # create a surface twice the size of the particle
        gs = pygame.Surface(r * 2)

        # draw a circle with a radius twice the size of the particle in the center of the new surface
        pygame.draw.circle(gs, (60, 20, 60), r, r.x)

        # blit the new larger particle on the primary display with the center of the smaller particle
        # use BLEND_RGB_ADD to increase luminosity if particles overlap
        PDS.blit(gs, s.xy - r, special_flags=pygame.BLEND_RGB_ADD)

def burst(xy, verticies, ricochet_direction):
    global parts

    for i in range(20):
        if verticies == 0: # horizontal particle burst
            v = V(uniform(-4, -2) if i // 10 else uniform(2, 4), uniform(1, 2) if ricochet_direction else uniform(-5, -4))
        else:
            v = V(uniform(1, 2) if ricochet_direction else uniform(-2, -1), uniform(-4, -2) if i // 10 else uniform(5, 4))
        parts += [particle(xy, v)]

WHITE = (255, 255, 255)
RED = (255, 0, 0)

pygame.init()
PDS = pygame.display.set_mode()
PDR = PDS.get_rect()
FPS = 120

GRAVITY = 0.1

parts = []
ball = V(PDR.center)
rad = 80
v = V()
f = V()

pressed = False
pressed_timer = None

dts = time.time()
exit_demo = False
while not exit_demo:
    for e in pygame.event.get():
        if e.type == KEYDOWN and e.key == K_ESCAPE:
            exit_demo = True

    now = time.time()
    dt = (now - dts) * FPS
    dts = now

    mp = V(pygame.mouse.get_pos())
    dist = mp.distance_to(ball)

    mb = pygame.mouse.get_pressed()
    if mb[0] and not pressed:
        if dist <= rad:
            pressed = True
            pressed_timer = time.time()
    if pressed:
        if not mb[0]:
            if dist > rad:
                deg = V().angle_to(mp - ball)
                a = V(1, 0)
                b = a.rotate(deg + 180) * (dist - rad)
                v = b / 10
            pressed = False
        if now - pressed_timer > 4:
            exit_demo = True

    ball += v * dt
    if v.x != 0 or v.y != 0:
        a = v.normalize()
        v -= (a / 10) * dt
    if ball.x + rad > PDR.w: # RIGHT
        ball.x = PDR.w - rad
        v.x = -v.x
        burst(ball + (rad, 0), 1, 0)
    if ball.x - rad < 0: # LEFT
        ball.x = rad
        v.x = -v.x
        burst(ball - (rad, 0), 1, 1)
    if ball.y + rad > PDR.h: # BOTTOM
        ball.y = PDR.h - rad
        v.y = -v.y
        burst(ball + (0, rad), 0, 0)
    if ball.y - rad < 0: # TOP
        ball.y = rad
        v.y = -v.y
        burst(ball - (0, rad), 0, 1)

    PDS.fill(0)
    # create a container to hold particles that need deleting

    kill_parts = []
    for p in parts:
        p.update() # draw and update postion/size of the particle

        # if the particle is outside of the PDS or the radius is less than zero ie no longer visible
        # then add it the killparticles pile
        if p.xy.y >= PDR.bottom or p.radius <= 0:
            kill_parts += [p]

    for p in kill_parts:
        parts.remove(p)

    if pressed and dist > rad:
        pygame.draw.line(PDS, RED, ball, mp)
    pygame.draw.circle(PDS, WHITE, ball, rad)

    pygame.display.update()
pygame.quit()
sys.exit()