6. Random pixels

6.1. Random pixel and random brightness

The following random functions can be used to create random pixels of random brightness.

6.2. Random pixel randint

random.randint(a, b): Return a random integer from a to b, including both.

The code below displays a random pixel of random brightness every 50ms, then clears the display before showing the next one.

from microbit import *
import random

while True:
    random_brightness = random.randint(1, 9)
    random_x = random.randint(0, 4)
    random_y = random.randint(0, 4)
    display.set_pixel(random_x, random_y, random_brightness)
    sleep(50)
    display.clear()

Tasks

Modify the code to restrict the brightness to 1 to 5, and the pixels to the central 9 pixels.

6.3. Tuple unpacking using an asterisk in a function call

Unpacking a tuple means splitting the tuple’s elements into individual variables.
From the code above, the three lines of code that generate the random values can be moved into a function that returns the three random values in a tuple.
The code below, uses the function, rand_pix(), to return a tuple of arguments for the set_pixel method.
Tuple unpacking is used to unpack the tuple returned by the function, rand_pix(), for the set_pixel method.
The returned tuple, (random_x, random_y, random_brightness), is unpacked by *rand_pix(), so that random_x, random_y, random_brightness are used as arguments.
An asterisk * is used for unpacking positional arguments during the function call.

from microbit import *
import random

def rand_pix():
    random_brightness = random.randint(1, 9)
    random_x = random.randint(0, 4)
    random_y = random.randint(0, 4)
    return (random_x, random_y, random_brightness)

while True:
    display.set_pixel(*rand_pix())
    sleep(50)
    display.clear()

Tasks

Modify the function, rand_pix(), to restrict the brightness to 4 to 7, and the pixels to the bottom 2 rows.

6.4. Tuple unpacking in multiple assignment

Instead of unpacking the returned tuple in the function call, multiple assignment is used in tuple unpacking.
Tuple unpacking is used to unpack the returned tuple into 3 variables:
random_x, random_y, random_brightness = rand_pix().
These variables can then be passed into the set_pixel method:
display.set_pixel(random_x, random_y, random_brightness).

from microbit import *
import random

def rand_pix():
    random_brightness = random.randint(1, 9)
    random_x = random.randint(0, 4)
    random_y = random.randint(0, 4)
    return (random_x, random_y, random_brightness)

while True:
    random_x, random_y, random_brightness = rand_pix()
    display.set_pixel(random_x, random_y, random_brightness)
    sleep(50)
    display.clear()

Tasks

Modify the function, rand_pix(), to restrict the brightness to 3 to 6, and the pixels to the top 2 rows.

6.5. Random pixel randrange(stop)

random.randrange(stop): Return a randomly selected integer from zero and up to (but not including) stop.

The code below uses randrange for the x and y values.

random.randrange(5) returns values from 0 to 4.

from microbit import *
import random

def rand_pix():
    random_brightness = random.randint(1, 9)
    random_x = random.randrange(5)
    random_y = random.randrange(5)
    return (random_x, random_y, random_brightness)

while True:
    random_x, random_y, random_brightness = rand_pix()
    display.set_pixel(random_x, random_y, random_brightness)
    sleep(50)
    display.clear()

Tasks

Modify the function, rand_pix(), to restrict the brightness to 3 to 6, and the pixels to the left 3 columns.

6.6. Random pixel randrange(start, stop)

random.randrange(start, stop): Return a randomly selected integer from start and up to (but not including) stop.

The code below uses randrange to restrict the x and y values to the inner square of 9 pixels.

from microbit import *
import random

def rand_pix():
    random_brightness = random.randint(1, 9)
    random_x = random.randrange(1, 4)
    random_y = random.randrange(1, 4)
    return (random_x, random_y, random_brightness)

while True:
    random_x, random_y, random_brightness = rand_pix()
    display.set_pixel(random_x, random_y, random_brightness)
    sleep(50)
    display.clear()

Tasks

Modify the function, rand_pix(), to restrict the brightness to 1 to 3, and the pixels to the right 3 columns in the bottom 4 rows.

6.7. Random pixel randrange(start, stop, step)

random.randrange(start, stop, step): Return a randomly selected element from start and up to (but not including) stop in steps of step.

The code below uses randrange to restrict the x and y values to rows and columns 0, 2, 4.

The display is not cleared so that all the pixels that are set are shown.

from microbit import *
import random

def rand_pix():
    random_brightness = random.randint(1, 9)
    random_x = random.randrange(0, 5, 2)
    random_y = random.randrange(0, 5, 2)
    return (random_x, random_y, random_brightness)

while True:
    random_x, random_y, random_brightness = rand_pix()
    display.set_pixel(random_x, random_y, random_brightness)
    sleep(50)
    display.clear()

Tasks

Modify the function, rand_pix(), to restrict the brightness to 1 to 3, and the pixels to columns 1 and 3 and the rows to 1 and 3.

6.8. Random pixel random.choice

random.choice(seq): Return a random element from the non-empty sequence seq such as a list or tuple.

The code below uses random.choice to choose the x and y values from 1, 2 and 3.
The brightness is chosen from values, 1, 5, and 9.
The display is not cleared so that all the pixels that are set are shown.

from microbit import *
import random

while True:
    random_brightness = random.choice((1, 5, 9))
    random_x = random.choice((1, 2, 3))
    random_y = random.choice((1, 2, 3))
    display.set_pixel(random_x, random_y, random_brightness)
    sleep(50)

Tasks

Modify the code above to use a fucntion, rand_pix(), to restrict the brightness to 1, 3 or 5, and the pixels to columns 0, 3, and 4 and the rows to 1 and 3.

6.9. Random Pixel rows and columns

The code below sets the brightness to 9 for a pixel in each row, with the column being random for each pixel.

from microbit import *
import random

def rand_x():
    return random.randint(0, 4)

while True:
    for y in range(0, 5):
        display.set_pixel(rand_x(), y, 9)
    sleep(200)
    display.clear()

Tasks

Write code to set the brightness to 9 for a pixel in each column, with the row being random for each pixel.

6.10. Random Pixels

The code below sets the brightness to 9 for 3 pixels in random rows and random columns.
Note the use of the underscore, _, as a throw away variable, in for _ in range(0, 3).
A single underscore is used in place of a variable whose value is not going to be used in a loop.

from microbit import *
import random

def rand_val():
    return random.randint(0, 4)

while True:
    for _ in range(3):
        display.set_pixel(rand_val(), rand_val(), 9)
    sleep(200)
    display.clear()

Tasks

Modify the code above to produce 10 random pixels at a time.
Change the brightness to 5, and explore how many random pixels are needed so that only 1 to 3 pixels are left turned off.

6.11. Random Pixels choice Pixel rows and columns lists

Lists can be used to restrict the possible x or y values.
The function, rand_val(vals), chooses one random value from the list passed to it.
In the code below, there are a total of 9 pixels that can be used. 2 random pixels are shown at a time.

from microbit import *
import random

xvals = [0, 2, 4]
yvals = [0, 2, 4]

def rand_val(vals):
    return random.choice(vals)

while True:
    for _ in range(2):
        display.set_pixel(rand_val(xvals), rand_val(yvals), 5)
    sleep(200)
    display.clear()

Tasks

Adjust the code to restrict the possible x and y values to the central 3 x 3 square, while showing 3 random pixels at a time.

6.12. get_pixel and set_pixel

display.get_pixel(x, y) == 0 can be used to check if a pixel is on or off.

get_pixel(x, y): Return the brightness of pixel at column x and row y as an integer between 0 and 9.

The definition below checks each pixel to see if it is off and returns True if all are on.

As soon as it finds a pixel that is off, it returns False.

from microbit import *

def full_screen_on_check():
    for y in range(0, 5):
        for x in range(0, 5):
            if display.get_pixel(x, y) == 0:
                return False
    return True

The code below creates changing displays of random pixels.
Start by just importing the randint function from the random module.
full_screen_on_check() checks to see when the display has been filled with 25 pixels.
fill_screen_with_counter turns on random pixels with brightness between 5 and 9. It checks to see if the screen is filled, and returns the number of random pixels used in the process.
The number of random pixels used to fill the screen is then scrolled.

from microbit import *
from random import randint

def full_screen_on_check():
    for y in range(0, 5):
        for x in range(0, 5):
            if display.get_pixel(x, y) == 0:
                return False
    return True

def fill_screen_with_counter():
    counter = 0
    while True:
        counter += 1
        x = randint(0, 4)
        y = randint(0, 4)
        brightness = randint(1, 4)
        display.set_pixel(x, y, brightness)
        if full_screen_on_check():
            return counter
        sleep(30)

while True:
    new_fill_count = fill_screen_with_counter()
    display.scroll(new_fill_count)
    sleep(1000)

Tasks

Add code to display the min and max counts obtained in the code above.
Improve the code in answer to task 1, by creating definitions to update the min and max counts, and to display the counts on button pressing. The main loop should look like this:
Improve the code in answer to task 2, by adding a set to keep track of displayed pixels in the function, fill_screen_with_counter(). Number the pixels 0 to 4 in the top row, 5 to 9 in the next row. etc. Check to see if the length of the set is 25 to tell that the screen is full.
counts = [None, None] while True: new_fill_count = fill_screen_with_counter() counts = update_counts(counts, new_fill_count) display_counts(counts, new_fill_count) sleep(1000) display.clear()

Q1

Add code to display the min and max counts obtained in the code above.

from microbit import *
from random import randint

def full_screen_check():
    for y in range(0, 5):
        for x in range(0, 5):
            if display.get_pixel(x, y) == 0:
                return False
    return True

def fill_screen_with_counter():
    counter = 0
    while True:
        counter += 1
        x = randint(0, 4)
        y = randint(0, 4)
        brightness = randint(1, 4)
        display.set_pixel(x, y, brightness)
        if full_screen_check():
            return counter
        sleep(30)

min_fill_count = None
max_fill_count = None

while True:
    new_fill_count = fill_screen_with_counter()
    display.scroll(new_fill_count, delay=60)
    if min_fill_count is not None:
        min_fill_count = min(min_fill_count, new_fill_count)
    else:
        min_fill_count = new_fill_count
    if max_fill_count is not None:
        max_fill_count = max(max_fill_count, new_fill_count)
    else:
        max_fill_count = new_fill_count
    display.scroll(min_fill_count, delay=60)
    display.scroll(max_fill_count, delay=60)
    sleep(1000)

Q2

Improve the code in answer to task 1, by creating definitions to update the min and max counts, and to display the counts on button pressing.

from microbit import *
from random import randint


def full_screen_check():
    for y in range(0, 5):
        for x in range(0, 5):
            if display.get_pixel(x, y) == 0:
                return False
    return True


def fill_screen_with_counter():
    counter = 0
    while True:
        counter += 1
        x = randint(0, 4)
        y = randint(0, 4)
        brightness = randint(1, 4)
        display.set_pixel(x, y, brightness)
        if full_screen_check():
            return counter
        sleep(10)


def update_counts(counts, count):
    min_fill_count = counts[0]
    if min_fill_count is not None:
        min_fill_count = min(min_fill_count, count)
    else:
        min_fill_count = count
    max_fill_count = counts[1]
    if max_fill_count is not None:
        max_fill_count = max(max_fill_count, count)
    else:
        max_fill_count = count
    return (min_fill_count, max_fill_count)


def display_counts(counts, new_fill_count):
    if button_a.was_pressed():
        display.scroll(new_fill_count, delay=60)
    if button_b.was_pressed():
        display.scroll(counts[0], delay=60)
        display.scroll(counts[1], delay=60)


counts = [None, None]

while True:
    new_fill_count = fill_screen_with_counter()
    counts = update_counts(counts, new_fill_count)
    display_counts(counts, new_fill_count)
    sleep(1000)
    display.clear()

Q3

Improve the code in answer to task 2, by adding a set to keep track of displayed pixels in the function, fill_screen_with_counter(). Number the pixels 0 to 4 in the top row, 5 to 9 in the next row. etc. Check to see if the length of the set is 25 to tell that the screen is full.

from microbit import *
from random import randint
import utime


def full_screen_check():
    for y in range(0, 5):
        for x in range(0, 5):
            if display.get_pixel(x, y) == 0:
                return False
    return True


def fill_screen_with_counter():
    counter = 0
    screenset = set()
    while True:
        counter += 1
        x = randint(0, 4)
        y = randint(0, 4)
        brightness = randint(1, 4)
        display.set_pixel(x, y, brightness)
        screenset.add(x + y*5)
        if len(screenset) == 25:
            return counter
        sleep(1)


def update_counts(counts, count):
    min_fill_count = counts[0]
    if min_fill_count is not None:
        min_fill_count = min(min_fill_count, count)
    else:
        min_fill_count = count
    max_fill_count = counts[1]
    if max_fill_count is not None:
        max_fill_count = max(max_fill_count, count)
    else:
        max_fill_count = count
    return (min_fill_count, max_fill_count)


def display_counts(counts, new_fill_count):
    if button_a.was_pressed():
        display.scroll(new_fill_count, delay=60)
    if button_b.was_pressed():
        display.scroll(counts[0], delay=60)
        display.scroll(counts[1], delay=60)


counts = [None, None]

while True:
    new_fill_count = fill_screen_with_counter()
    counts = update_counts(counts, new_fill_count)
    display_counts(counts, new_fill_count)
    sleep(1)
    display.clear()

Note

Sets can be good to use when checking somethings since members of the set cannot be be repeated. Adding a member to a set that already exists has no affect.