Merry Christmas: particles in pygame with python

Merry Christmas everyone with this little script to show some fun Christmas particles with pygame.

A merry Christmas… with pygame

#!/usr/bin/python3.4
import pygame, sys, random
from pygame.locals import *


pygame.init()
pygame.mixer.init()
screen = pygame.display.set_mode((1376, 900),0,32)
clock = pygame.time.Clock()
pygame.mixer.music.load("christmas.mp3")
pygame.mixer.music.play()
trees = pygame.image.load("trees.png").convert()
pygame.display.set_caption('Fireworks')
# [loc, velocity, timer]
particles = []
pygame.mouse.set_visible(False)

# ======================================= FPS ====
font = pygame.font.SysFont("Arial", 20)
def show_fps():
    "shows the frame rate on the screen"
    # global clock

    fr = str(int(clock.get_fps()))
    frt = font.render(fr, 1, pygame.Color("coral"))
    screen.blit(frt, (0, 0)) 

class Particles:
    def __init__(self):
        pass

def particles_gen(pnum):
    for i in range(pnum):
        mx, my = pygame.mouse.get_pos()
        particles.append([
            # actual Position
            [mx, my],
            # direction
            [random.randint(0, 42) / 6 - 30.5, 
            random.randint(0, 42) / 6 - 3.5],
            # radius random shape
            random.randint(4, 6)])
    move_particles(particles)


def randomcolor():
    a, b, c = (random.randrange(0,255), random.randrange(0,255), random.randrange(0,255))
    return a, b, c

def move_particles(particles):
    for particle in particles:
        particle[0][0] += particle[1][0] # new position + dir x
        particle[0][1] += particle[1][1] # new pos + dir y
        particle[2] -= 0.035 # shrinking
        particle[1][1] += 0.15 # falls down same speed
        # this conditions to remove unseen particles optimize the velocity
        conditions = particle[0][0] < 0 or particle[0][0] > 1376 or particle[0][1] > 900 or particle[0][1] < 0
        particles.remove(particle) if (particle[2] == 0 or conditions) else pygame.draw.circle(screen, randomcolor(), [int(particle[0][0]), int(particle[0][1])], int(particle[2]))

# ==================== Makes things go on ====
sx = 0 # scrolling variable
while True:
    
    # screen.fill((0,0,0)) # fills the screen in black
    sx -= 1
    screen.blit(trees, (sx, 0))
    screen.blit(trees, (sx + 1376, 0))
    if sx == - 1376:
        sx = 0
    particles_gen(pnum=50)
    show_fps()
    # ========= FPS ============
    # Buttons ------------------- #
    for event in pygame.event.get():
        if event.type == pygame.QUIT or (
            event.type == pygame.KEYDOWN 
            and event.key== pygame.K_ESCAPE):
            pygame.quit()

    pygame.display.flip()
    clock.tick(60)