PyGame - Drag Rectangles

#!/usr/bin/env python3

#
# pygame (simple) template - by furas
#
# https://github.com/furas/my-python-codes/tree/master/pygame/__template__/
#

# ---------------------------------------------------------------------

__author__  = 'Bartlomiej "furas" Burek'
__webpage__ = 'http://blog.furas.pl'

# ---------------------------------------------------------------------

import pygame

# === CONSTANS === (UPPER_CASE names)

BLACK = (  0,   0,   0)
WHITE = (255, 255, 255)

RED   = (255,   0,   0)
GREEN = (  0, 255,   0)
BLUE  = (  0,   0, 255)

SCREEN_WIDTH  = 600
SCREEN_HEIGHT = 400

BLOCK_SIZE = 50

# === CLASSES === (CamelCase names)

'''
class Button():
'''

# === FUNCTIONS === (lower_case names)

    # empty

# === MAIN === (lower_case names)

# --- (global) variables ---

# --- init ---

pygame.init()

screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))
screen_rect = screen.get_rect()

# --- objects ---

'''
button = Button(...)
'''

rects = []

for x in range(10):
    rects.append( pygame.Rect(x*(BLOCK_SIZE+5), BLOCK_SIZE, BLOCK_SIZE, BLOCK_SIZE) )

selected = None

# --- mainloop ---

clock = pygame.time.Clock()
is_running = True

while is_running:

    # --- events ---

    for event in pygame.event.get():

        # --- global events ---

        if event.type == pygame.QUIT:
            is_running = False

        elif event.type == pygame.KEYDOWN:
            if event.key == pygame.K_ESCAPE:
                is_running = False

        elif event.type == pygame.MOUSEBUTTONDOWN:
            if event.button == 1:
                for i, r in enumerate(rects):
                    if r.collidepoint(event.pos):
                        selected = i
                        selected_offset_x = r.x - event.pos[0]
                        selected_offset_y = r.y - event.pos[1]

        elif event.type == pygame.MOUSEBUTTONUP:
            if event.button == 1:
                selected = None

        elif event.type == pygame.MOUSEMOTION:
            if selected is not None: # selected can be `0` so `is not None` is required
                # move object
                rects[selected].x = event.pos[0] + selected_offset_x
                rects[selected].y = event.pos[1] + selected_offset_y

        # --- objects events ---

        '''
        button.handle_event(event)
        '''

    # --- updates ---

        # empty

    # --- draws ---

    screen.fill(BLACK)

    '''
    button.draw(screen)
    '''

    # draw rect
    for r in rects:
        pygame.draw.rect(screen, RED, r)

    pygame.display.update()

    # --- FPS ---

    clock.tick(25)

# --- the end ---

pygame.quit()