13. for-loops

13.1. for-loops with strings

Python can loop through each character in a string and do something with it.

for character in welcome_string takes each character in the string Hello and puts it in the variable character.

from microbit import *

welcome_string = 'Hello'
while True:
    for character in welcome_string:
        display.scroll(character)
        sleep(300)

Using a for-loop allows other actions on each character or between each character in the string.

The code below scrolls each character in the string Hello and puts another character between them.

from microbit import *

welcome_string = 'Hello'
gap_character = "-"
while True:
    for character in welcome_string:
        display.scroll(character)
        display.show(gap_character)
        sleep(300)

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Tasks

1. Write a for-loop to scroll each letter in ‘ace’ individually and show a “-” between them.

2. Write a for-loop to scroll each digit in ‘123’ individually and show a “*” between them.

3. Write a for-loop to scroll each letter in the word ‘Hello’ and show a happy face image after each letter.

4. Write a for-loop to scroll each letter in ‘christmas’ and show a XMAS image after each letter.

Q1

Write a for-loop to scroll each letter in ‘ace’ individually and show a “-” between them.

from microbit import *

string = 'ace'
gap_character = "-"
while True:
    for character in string:
        display.scroll(character)
        display.show(gap_character)
        sleep(300)

Q2

Write a for-loop to scroll each digit in ‘123’ individually and show a “*” between them.

from microbit import *

string = '123'
gap_character = "*"
while True:
    for character in string:
        display.scroll(character)
        display.show(gap_character)
        sleep(300)

Q3

Write a for-loop to scroll each letter in the word ‘Hello’ and show a happy face image after each letter.

from microbit import *

# A string with the word "Hello"
word = "Hello"

# Loop through each letter in the word
for letter in word:
    # Scroll the letter on the display quickly
    display.scroll(letter, delay=50)
    # Show the HAPPY image for 300 ms
    display.show(Image.HAPPY)
    sleep(300)

Q4

Write a for-loop to scroll each letter in ‘christmas’ individually and show a XMAS image between them.

from microbit import *

# A string with the word "Christmas"
word = "Christmas"

# Loop through each letter in the word
for letter in word:
    # Scroll the letter on the display quickly
    display.scroll(letter, delay=50)
    # Show the XMAS image for 300 ms
    display.show(Image.XMAS)
    sleep(300)

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13.2. for-loops with lists

Python can loop through each element in a list and do something with it.

In the code below, each element in the list is displayed.

from microbit import *

tennis_champs = ['Novak', 'Rafael', 'Roger']
while True:
    for tennis_star in tennis_champs:
        display.scroll(tennis_star, delay=80)
    sleep(300)

In the code below, each number in the list is displayed.

from microbit import *

primes = [2, 3, 5, 7]
while True:
    for num in primes:
        display.show(num)
        sleep(300)

---

Tasks

1. Write a for-loop to scroll each car in the list ['Lotus', 'Shelby', 'Porsche'].

2. Write a for-loop to scroll each number in the list [1, 2, 3, 5, 8].

Q1

Write a for-loop to scroll each car in the list ['Lotus', 'Shelby', 'Porsche'].

from microbit import *

cars_list = ['Lotus', 'Shelby', 'Porsche']
while True:
    for car in cars_list:
        display.scroll(car)
    sleep(300)

Q2

Write a for-loop to scroll each number in the list [1, 2, 3, 5, 8].

from microbit import *

num_list = [1, 2, 3, 5, 8]
while True:
    for num in num_list:
        display.scroll(num)
    sleep(300)

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13.3. Conditions within for-loops with lists

What does this code do?

test_num % num gets the remainder from division.

Which numbers in the list are factors of 42?

from microbit import *

primes = [2, 3, 5, 7]
test_num = 42
while True:
    for num in primes:
        if test_num % num == 0:
            display.scroll(num, delay=50)
    sleep(300)

---

Tasks

1. Write a for-loop to scroll the prime factors of 63 from a list of the first 4 primes.

2. Write a for-loop to scroll the even numbers in the list of squares [1, 4, 9, 16, 25, 36].

Q1

Write a for-loop to scroll the prime factors of 63 from a list of the first 4 primes.

from microbit import *

primes = [2, 3, 5, 7]
test_num = 63
while True:
    for num in primes:
        if test_num % num == 0:
            display.scroll(num, delay=50)
    sleep(300)

Q2

Write a for-loop to scroll the even numbers in the list of squares [1, 4, 9, 16, 25, 36].

from microbit import *

num_list = [1, 4, 9, 16, 25, 36]
while True:
    for num in num_list:
        if num % 2 == 0:
            display.scroll(num, delay=50)
    sleep(300)