2. Functions for the microbit

2.1. Functions with parameters

Functions can be more flexible when they use parameters.
A parameter is the variable in the parentheses of the function which allows information to be passed to the function.
An argument is the value in the parentheses that is sent to the function when it is called.
In the code below, name is the parameter, and "beginner" and "user" are the arguments.
Text joins are carried out with a + between the text strings.

from microbit import *

def show_welcome(name):
    display.scroll("Hello " + name, delay=60)

show_welcome("beginner")
show_welcome("user")

Tasks

Write a function called ask_play_again with a parameter for their player_name, and display an example using it.

2.2. Functions with default parameters

Default values can be added to parameters. e.g. name=”Novice”

Text joins are carried out with a + between the text strings.

str() is used to turn score, which is a integer, into a string.

from microbit import *

def player_info(name="Novice", score=0):
    display.scroll(name + " has a score of " + str(score), delay=80)

player_info()
player_info("Rookie", 100)

Tasks

Write a function called player_health with 2 default parameters for their user_name and their game health status and display an example using the defaults and an example passing values.

2.3. Order with named parameters

When named parameters are used, their order is not important.

from microbit import *

def player_info(name="Novice", score=0):
    display.scroll(name + "  a score of " + str(score), delay=80)

player_info(name="Rookie", score=10)
player_info(score=10, name="Rookie")

Tasks

Write a function called player_health with 2 default parameters for their user_name and their game health status and display an example using it with the parameter order mixed up.

2.4. Parameter order: positional before default

Non-default parameters have to come before default parameters.

e.g in the code below, the name parameter (without a default value) must come before the score parameter (with a default value).

from microbit import *

def player_info(name, score=0):
    display.scroll(name + " has a score of " + str(score), delay=80)

player_info("novice")
player_info("Rookie", 100)

Tasks

Write a function called player_health which takes the user_name as the first parameter and their game health status as a default parameter and display an example using it with and without passing a value to the default parameter.

Tasks

Write a function called player_info with 3 default parameters for their user_name, their number of game lives and their game health status and display an example using it.

2.5. Functions returning information

Functions can be more powerful by returning values.
The return value is what the function passes back to the code that called it.
Below is an example of a function that takes one parameter, the number of inches, and returns the number of centimetres.

from microbit import *

def convert_inches_to_centimetres(inches):
    return inches * 2.54

length_cm = convert_inches_to_centimetres(8)
display.scroll(length_cm)

Below is an example of a function that takes two parameters, the length and width of a rectangle, and returns the area.

from microbit import *

def area_of_rectangle(length, width):
    return length * width

area = area_of_rectangle(9, 7)
display.scroll(area)

Below is an example of a function that takes two parameters and returns a string.
Text joins are carried out with a + between the text strings.
str() is used to turn age, which is a integer, into a string.

from microbit import *


def player_goals(name, goals):
    return name + " scored " + str(goals) + " goals."

display.scroll(player_goals("Cristiano Ronaldo", 838), delay=70)
display.scroll(player_goals("Messi", 803), delay=70)
display.scroll(player_goals("Pele", 762), delay=70)

Tasks

Define a function convert_cm_to_m(cm) that returns the result of converting a length in cm to metres.
Define a function convert_m_to_cm(m) that returns the result of converting a length in metres to cm.
Define a function area_square(length) that returns the area of a square.
Write a function called random_greeting that returns a random greeting that is randomly chosen from a list of greetings: ["Hi", "Hello", "G'day"]. See: https://www.w3schools.com/python/ref_random_choice.asp

2.6. Allowing for a variable number of arguments

*args allow a function to take any number of positional arguments (non keyword arguments).

*nums allows a variable number of arguments to be passed in to be added in the multi_add function.
In the function, nums is a tuple of the arguments.
For multi_add(1, 3, 5, 7, 9), nums is the tuple (1, 3, 5, 7, 9).

from microbit import *


def multi_add(*nums):
    sum = 0
    for num in nums:
        sum = sum + num
    return sum


display.scroll(multi_add(1, 3, 5, 7, 9), delay=70)

Tasks

Define a function multi_product(*nums) that finds the product of the first 4 primes.
Define a function multi_average(*nums) that finds the average of the first 4 primes.

2.7. Spy codes

The code below converts a code string into a message string.

This can be refactored to use a defintion block with parameters that might make it more useful.

from microbit import *

secret_string = 'hqz'
while True:
    for character in secret_string:
        # convert the string character to an ascii number
        asciinum = ord(character)
        # subtract 2 from the acscii number
        asciinum +=2
        # convert the ascii number to a string character
        newchar = chr(asciinum)
        # scroll the secret character
        display.scroll(newchar, delay=50)
    sleep(300)

Refactored code:

from microbit import *


def get_code_message(secret_string, shifter):
    code_message = ''
    for character in secret_string:
        # convert the string character to an ascii number
        asciinum = ord(character)
        # subtract shifter from the acscii number
        asciinum +=shifter
        # convert the ascii number to a string character
        newchar = chr(asciinum)
        # add the newchar
        code_message += newchar
    return code_message

secret_string = 'hqz'
code_message = get_code_message(secret_string, -2)
while True:
    display.scroll(code_message, delay=50)
    sleep(300)

Further modifications can be made.
The text can be converted to upper case so all code messages are in upper case.
The shifter value can be restricted to a number between 0 and 25 by getting the remainder after dividing it by 26.
All characters that are not standard letters are unchanged, including spaces and punctuation and numbers.

from microbit import *


# A function to encrypt a message using a shift cipher with a given shifter
def get_shift_cipher(secret_string, shifter):
    # Use mod 26 to keep the shifter within the range of the alphabet
    shifter = shifter % 26
    # Initialize an empty string for the cipher
    cipher = ""
    # Convert the secret string to uppercase
    secret_string = secret_string.upper()
    # Loop through each character in the secret string
    for character in secret_string:
        # Convert the character to an ascii number
        asciinum = ord(character)
        # If the ascii number is between 65 and 90 (A-Z), apply the shift
        if asciinum>=65 and asciinum<=90:
            asciinum += shifter
            # If the ascii number is less than 65, cycle it back to the range 65-90
            if asciinum<65:
                asciinum += 26
            # If the ascii number is greater than 90, cycle it back to the range 65-90
            elif asciinum>90:
                asciinum -= 26
            # Convert the ascii number back to a character and append it to the cipher
            cipher += chr(asciinum)
        # If the ascii number is not between 65 and 90, keep it unchanged and append it to the cipher
        else:
            cipher += character
    # Return the cipher
    return cipher

# A sample secret string and shifter to test the function
secret_string = 'hqz'
code_message = get_shift_cipher(secret_string, 2)
# Loop forever
while True:
    # Scroll the code message on the display with a delay of 50 ms
    display.scroll(code_message, delay=50)
    # Pause for 300 ms
    sleep(300)

Tasks

Make use of the get_shift_cipher function to decode this secret code: ‘AMBC PCB. YZMPR KGQQGML!’. Set the shifter to 2.

Exercise

Here is a code message. “EWWL SL LZW KSXWZGMKW. TJAFY LZW HSUCSYW. OSLUZ QGMJ TSUC.” The shifter value has been lost. Can you try out all shifter values to read the message? Can you find the value of the shifter and use it to decode this second message: “LZW KLGJE AK UGEAFY.”