Task_15_functions.md

Task 15 - Functions and arguments

A function groups reusable code. You define it with def, give it a name, and list any parameters inside parentheses.

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Demo 1 - Simple function, no parameters

def hello_world():
    print("Hello, World!")

hello_world()     # call the function

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Demo 2 - Positional and keyword arguments

def greeting(first_name, last_name):
    print(f"Hello, {first_name} {last_name}!")

greeting("John", "Doe")                 # positional
greeting(first_name="Jane", last_name="Doe")   # keyword

All required parameters must be supplied, either by position or by name.

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Demo 3 - Returning a value

def get_greeting(name):
    return f"Hi {name}"

message = get_greeting("John")    # store the result
print(message)

A function can perform a task (print) or return a value (for later use).

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Demo 4 - Default and variable arguments

def decrement(number, by=1):      # by has a default
    return number - by

print(decrement(10))              # uses default -> 9
print(decrement(10, by=3))        # override default -> 7

def multiply(*numbers):           # * collects any count of arguments
    total = 1
    for number in numbers:
        total *= number
    return total

print(multiply(1, 2, 3, 4))       # 24

• Parameters with = get default values.
• A star * before a name creates a tuple of all extra positional arguments.

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Your exercise

1. Create a file called Task_15.py.

2. Write a function add(x, y) that returns the sum of its two arguments.

3. Write a function power(base, exponent=2) that returns base raised to exponent.

   • Call it once with one argument (power(5)) and once with two arguments (power(2, 3)) and print both results.

4. Write a function average(*scores) that returns the arithmetic mean of any number of scores.

   • Call it with three different sets of arguments and print each average.

5. Add a short print_help() function that prints a one-line description of how to use the program.

   • At the bottom of the file, call print_help() so the description shows whenever someone runs the script.

Run Task_15.py and verify that each function behaves as specified.