Supposed test case for GC failure.

waves.py

""" Display endless waves on the LED display.

    You can press the left button to have the waves go faster,
    the right button to slow down things.

    MAL 2016-01-06.

"""
import microbit
import math

# Array of LED brightness levels (0=off, 8=on); rows and columns
# correspond to the LEDs on the Microbit, e.g. leds[0][2] maps
# to the second LED in the first row.
leds = [[0] * 5 for i in range(5)]

def display_leds_image_string():
    
    img_string = '\n'.join(''.join('%i' % column
                                    for column in row)
                            for row in leds)
    img = microbit.Image(img_string)
    microbit.display.show(img)

def display_leds_image_array():
    
    img_array = bytearray()
    for row in leds:
        img_array.extend(bytearray(row))
    img = microbit.Image(5, 5, img_array)
    microbit.display.show(img)

def display_leds_set_pixel():
    
    for row in range(5):
        for column in range(5):
            # Note: The Microbit uses different indexing for LEDs
            microbit.display.set_pixel(column, row, leds[row][column])

#display_leds = display_leds_image_string
#display_leds = display_leds_image_array
display_leds = display_leds_set_pixel

def waves(delay):
    
    offset = 0
    while True:
        for row in range(5):
            for column in range(5):
                x = (row + offset) % 8 / 4 * math.pi
                leds[row][column] = int(
                    math.sin(x) * 4 + 4)
        display_leds()
        microbit.sleep(delay)
        offset += 1
        #print ('Offset: %i' % offset)
        print ('Offset: {}'.format(offset))
        if microbit.button_a.is_pressed():
            delay = max(0, delay - 10)
        if microbit.button_b.is_pressed():
            delay += 10

#waves(100)
waves(0)