Pydroid example

import pygame_sdl2
pygame_sdl2.import_as_pygame()
import pygame
import sys

# define some colors
BLACK = (0, 0, 0)
WHITE = (255, 255, 255)

# set up pygame
pygame.init()
DS = pygame.display.set_mode((640, 480))
CLOCK = pygame.time.Clock()

# frame per second
FPS = 120

# you can't set the width and height of the pygame window, it's
# fullscreen by default so you need to get the dimensions
W = DS.get_width()
H = DS.get_height()
HW, HH = int(W / 2), int(H / 2)

x = 0
dx = 4 # change this value to make the ball go faster or slower

while True:
    e = pygame.event.get()

    pygame.draw.circle(DS, WHITE, (x, HH), 30)

    x += dx
    if x > W or x < 0:
        dx = -dx
        x += dx

    pygame.display.update()
    DS.fill(BLACK)
    CLOCK.tick(FPS)