Example of a simple game with smooth keyboard movement of a ball around the screen. Uses pygame and Python.

app.py

import pygame

# Initialize pygame
pygame.init()

# Define colors
black = (0, 0, 0)

# Set the height and width of the screen
size=[800, 600]
screen=pygame.display.set_mode(size)

# Set title of screen
pygame.display.set_caption("My Game")

# Used to manage how fast the screen updates
clock=pygame.time.Clock()

#Load Image
ball = pygame.image.load("ball.png")

# Set speed, direction and position of ball
x_speed = 5
y_speed = 5

def handle_keypress(keys_pressed, velocity_x, velocity_y):
    if keys_pressed[pygame.K_LEFT]:
        velocity_x -= x_speed
    elif keys_pressed[pygame.K_RIGHT]:
        velocity_x += x_speed
    else:
        if velocity_x < 0:
            velocity_x += x_speed
            if velocity_x > 0:
                velocity_x = 0
        if velocity_x > 0:
            velocity_x -= x_speed
            if velocity_x < 0:
                velocity_x = 0

    if keys_pressed[pygame.K_UP]:
        velocity_y -= y_speed
    elif keys_pressed[pygame.K_DOWN]:
        velocity_y += y_speed
    else:
        if velocity_y < 0:
            velocity_y += y_speed
            if velocity_y > 0:
                velocity_y = 0
        if velocity_y > 0:
            velocity_y -= y_speed
            if velocity_y < 0:
                velocity_y = 0

    print(velocity_x, velocity_y)

    return (velocity_x, velocity_y)

def move(x_coord, y_coord, velocity_x, velocity_y):
    x_coord += velocity_x
    if x_coord < 0:
        x_coord = 0
        velocity_x = 0
    elif x_coord > size[0] - ball.get_width():
        x_coord = size[0] - ball.get_width()
        velocity_x = 0

    y_coord += velocity_y
    if y_coord < 0:
        y_coord = 0
        velocity_y = 0
    elif y_coord > size[1] - ball.get_height():
        y_coord = size[1] - ball.get_height()
        velocity_y = 0

    return (x_coord, y_coord, velocity_x, velocity_y)

# -------- Main Program Loop -----------
def game_loop():
    velocity_x = 0
    velocity_y = 0
    x_coord = 10
    y_coord = 10

    done = False
    while not done:
        for event in pygame.event.get(): # User did something
            if event.type == pygame.QUIT: # If user clicked close
                done=True # Flag that we are done so we exit this loop
            elif event.type == pygame.KEYDOWN and event.key == pygame.K_ESCAPE:
                done = True

        keys_pressed = pygame.key.get_pressed()
        velocity_x, velocity_y = handle_keypress(keys_pressed, velocity_x, velocity_y)
        x_coord, y_coord, velocity_x, velocity_y = move(x_coord, y_coord, velocity_x, velocity_y)

        #Clears the screen
        screen.fill(black)

        #Draw image onto screen
        screen.blit(ball, [x_coord, y_coord])

        # Limit to 20 frames per second
        clock.tick(20)

        # Go ahead and update the screen with what we've drawn.
        pygame.display.flip()

game_loop()
pygame.quit()