13. EXT: for-loops

13.1. Spacing characters

The code below scrolls each character in “a*c*e”, but does so by starting with ‘ace’ and “*” and uses them in a for-loop.
It uses indexing to get each character in the string ‘ace’ which is stored in the variable card_name. e.g. card_name[0] gets ‘a’.
It uses an if statement to check whether the loop is up to the last character so that it only adds ‘*’ if it is not the last character.

from microbit import *

card_name = 'ace'
string_length = len(card_name)
spacing_character = "*"
while True:
    for i in range(string_length):
        display.scroll(card_name[i])
        if i < string_length - 1:
            display.scroll(spacing_character)
    sleep(300)

Tasks

Write a for-loop to scroll each letter in ‘bot’ individually with a ‘|’ between them.
Write a for-loop to scroll each digit in ‘8850’ individually with a ‘+’ between them.

13.2. Code shifts

ASCII stands for American Standard Code for Information Interchange.
ASCII is a character encoding standard used in electronic communication to represent text. Each character (like letters, numbers, and symbols) is assigned a unique numeric value.
Characters can be converted to ASCII numbers, and back.

ord(character): returns the ASCII value for character.

e.g display.scroll(ord('a')) scrolls 97.

chr(number): returns the character for the ASCII number.

e.g display.scroll(chr(97)) scrolls ‘a’.

The code below converts the character to its ASCII number, decreases the ASCII number by 2, then converts the modified ASCII number back to a character.
e.g h is converted to ascii_num 104, 104 is changed to 102, then ascii_num 102 is converted to f.
‘h’ (ASCII 104) becomes ‘f’ (ASCII 102)
‘q’ (ASCII 113) becomes ‘o’ (ASCII 111)
‘z’ (ASCII 122) becomes ‘x’ (ASCII 120)

ord(character) converts the character to its ASCII number.
ascii_num -= 2 decreases the ASCII number by 2.
chr(ascii_num) converts the modified ASCII number back to a character.

from microbit import *

code_string = 'hqz'

while True:
    for character in code_string:
        ascii_num = ord(character)
        ascii_num -=2
        new_char = chr(ascii_num)
        display.scroll(new_char, delay=50)
    sleep(300)

Tasks

Write a for-loop that converts the code word “ald”, then scrolls the converted secret word “dog”.

13.3. Prime factors

The modulo operator % returns the remainder of a division operation.

dividend % divisor: returns the remainder when dividend is divided by divisor.

e.g 14 % 3 returns 2, because 14 divided by 3 is 4 with a remainder of 2.

e.g. 5 % 2 returns the remainder 1.
test_num % num returns the remainder from division.
if test_num % num == 0 checks whether the remainder is zero or not.

The code below scrolls the prime factors of 15, by only scrolling the divisor when the remainder is 0.

from microbit import *

primes = [2, 3, 5]
test_num = 15
while True:
    for num in primes:
        if test_num % num == 0:
            display.scroll(num, delay=50)
    sleep(300)

Tasks

Modify the code above to find the prime factors of 42.

13.4. Abbreviations

string[start: stop]: returns character start up to but not including character stop of the string.

'January'[0:3] returns characters 0 to 2 which is ‘Jan’.

The code below gets the first three letters of each month by using the slice month[0:3].

from microbit import *

months = ['January', 'February', 'March']
while True:
    for month in months:
        short_month = month[0:3]
        display.scroll(short_month, delay=80)
    sleep(300)

Tasks

Modify the code above to scroll the first 3 letters of the days: “Monday”, “Tuesday”, “Wednesday”.

13.5. Vowels

The keyword, in, can be used to test whether a character is in a string.

element in collection: returns True if element is found in collection, otherwise False.

"A" in "AEIOU" returns True.

element not in collection: returns True if element is not found in collection, otherwise False.

"B" not in "AEIOU" returns True.

What does this code do?
name[0] in "AEIOU" returns True if character 0 in the name string is in the string of vowels.
name[0] not in "AEIOU" returns True if character 0 in the name string is not in the string of vowels.

string.upper(): returns a new string with all characters converted to uppercase.

"hello world".upper() returns “HELLO WORLD”.

e.g. anna.upper() returns “ANNA”

The code below scrolls the name in upper case only if the name starts with a vowel.

from microbit import *

name_list = ['Alexia', 'Bethany', 'Chloe']
while True:
    for name in name_list:
        if name[0] in "AEIOU":
            display.scroll(name.upper(), delay=50)
    sleep(300)

The code below scrolls the name in upper case only if the name does not start with a vowel.

from microbit import *

name_list = ['Alexia', 'Bethany', 'Chloe']
while True:
    for name in name_list:
        if name[0] not in "AEIOU":
            display.scroll(name.upper(), delay=50)
    sleep(300)

sorted_list = sorted(original_list): returns a new list with the elements of original_list sorted in ascending order by default.

sorted_name_list = sorted([“Charlie”, “Alice”, “Bob”]) returns the list sorted_name_list which is [“Alice”, “Bob”, “Charlie”].

The code below sorts the list first then scrolls the name in uppercase.

from microbit import *

name_list = ['Zoe', 'Yasmin', 'Xena']
sorted_name_list = sorted(name_list)

while True:
    for name in sorted_name_list:
        display.scroll(name.upper(), delay=50)
    sleep(300)

Tasks

Write a for-loop to scroll names beginning with a vowel in [‘Gabriella’, ‘Julia’, ‘Isabel’, ‘Hannah’, ‘Emily’, ‘Fiona’, ‘Chloe’, ‘Daisy’, ‘Anna’, ‘Bella’]. Display the names in uppercase. Display the names in alphabetical order.

13.6. Storing values in a list

Storing values in a list allows you to keep track of the values that have been processed in a for-loop.

Exercises

Here is some fun code that displays a heart image as a series of 3 pixels. Change it from 3 to 5 pixels.
Here is some fun code that displays a heart image as a series of shown pixels. Change the pop parameter to pop the last item via -1 to clear the image in reverse.

Q1

Here is some fun code that displays a heart image as a series of 3 pixels. Change it from 3 to 5 pixels.

from microbit import *

heart = [
    [0, 1, 1, 1, 0],
    [1, 1, 1, 1, 1],
    [1, 1, 1, 1, 1],
    [0, 1, 1, 1, 0],
    [0, 0, 1, 0, 0]
]

lit_pixels = []  # Keep track of three active pixels

while True:
    for y in range(5):
        for x in range(5):
            if heart[y][x]:  # Only process active parts of the heart shape
                display.set_pixel(x, y, 9)
                lit_pixels.append((x, y))  # Store pixel coordinates

                # If more than 3 pixels are lit, remove the oldest one
                if len(lit_pixels) > 3:
                    old_x, old_y = lit_pixels.pop(0)
                    display.set_pixel(old_x, old_y, 0)

                sleep(100)

    sleep(500)
    display.clear()
    sleep(500)

Q2

Here is some fun code that displays a heart image as a series of shown pixels. Change the pop parameter to pop the last item via -1 to clear the image in reverse.

from microbit import *

heart = [
    [0, 1, 1, 1, 0],
    [1, 1, 1, 1, 1],
    [1, 1, 1, 1, 1],
    [0, 1, 1, 1, 0],
    [0, 0, 1, 0, 0]
]

lit_pixels = []  # Keep track of active pixels

while True:
    # Light up pixels one by one
    for y in range(5):
        for x in range(5):
            if heart[y][x]:  # Only process active parts of the heart shape
                display.set_pixel(x, y, 9)
                lit_pixels.append((x, y))  # Store pixel coordinates
                sleep(100)

    # Fade out pixels one by one instead of clearing all at once
    while lit_pixels:
        old_x, old_y = lit_pixels.pop(0)
        display.set_pixel(old_x, old_y, 0)
        sleep(100)

    sleep(500)

Q3

Here is some fun code that displays a heart image as a series of shown pixels, then clears it by choosing random pixels from the stored list of pixels. Modify it to dim the pixels instead of turning them off.

from microbit import *
import random  # Import random module

heart = [
    [0, 1, 1, 1, 0],
    [1, 1, 1, 1, 1],
    [1, 1, 1, 1, 1],
    [0, 1, 1, 1, 0],
    [0, 0, 1, 0, 0]
]

lit_pixels = []  # Keep track of active pixels

while True:
    # Light up pixels one by one
    for y in range(5):
        for x in range(5):
            if heart[y][x]:  # Only process active parts of the heart shape
                display.set_pixel(x, y, 9)
                lit_pixels.append((x, y))  # Store pixel coordinates
                sleep(100)

    # Remove pixels randomly instead of sequentially
    while lit_pixels:
        random_index = random.randint(0, len(lit_pixels) - 1)  # Get a random pixel index
        old_x, old_y = lit_pixels.pop(random_index)  # Remove a random pixel
        display.set_pixel(old_x, old_y, 0)
        sleep(50)

    sleep(500)