14. Functions

Functions are blocks of code that can be used many times in a program.
They avoid code repetition.
Functions can do something or return values.
Functions are defined using the def keyword.
To use the function, it is called using its name with parentheses.

14.1. Functions without parameters

The function below does something. It prints text.
It is defined using the def keyword and has empty parentheses.
The def line has a colon at the end and the code for the definition is indented.
To use the function, it is called using its name with parentheses; show_welcome().
def show_welcome():
    print("Hello python user!")



Without the return statement, the function will return None.


  1. Write a function called print_name that prints your name.

  2. Write a function called countdown that counts down from 5 to 1, printing each number.

14.2. Functions with parameters

Functions can be more powerful by using 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.
def show_welcome(name):
    print("Hello " + name)


14.3. Functions with default parameters

def employee_info(name="N. U. Guy", salary=20000):
    print(f"{name} earns ${salary} per year")

employee_info(name="Nu Guy", salary=25000)
employee_info("B. Ginner", 30000)


  1. 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 print an example using it.

14.4. 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.
def convert_inches_to_centimetres(inches):
    return inches * 2.54

length_cm = convert_inches_to_centimetres(8)
Below is an example of a function that takes two parameters, the length and width of a rectangle, and returns the area.
 def area_of_rectangle(length, width):
    return length * width

area = area_of_rectangle(9, 7)
Below is an example of a function that takes two parameters and returns a welcome message using the name and age of a person.
Text joins are carried out with a + between the text strings.
str() is used to turn age, which is a integer, into a string.
def name_age_greeting(name, age):
    return "Hello " + name + ", you are " + str(age) + " years old."

print(name_age_greeting("Peter", 21))
print(name_age_greeting("Paul", 24))
print(name_age_greeting("Mary", 19))


  1. Define a function convert_cm_to_m(cm) that returns the result of converting a length in cm to metres.

  2. Define a function convert_m_to_cm(m) that returns the result of converting a length in metres to cm.

  3. Define a function area_square(length) that returns the area of a square.

  4. 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

14.5. *args

*args allow a function to take any number of positional arguments (non keyword arguments).
*num allows a variable number of arguments to be passed in to be added in the multi_add function.
In the function, num is a tuple of the arguments.
For multi_add(2,5), num is the tuple`` (2, 5)``.
For multi_add(1, 3, 5, 7, 9), num is the tuple (1, 3, 5, 7, 9).
def multi_add(*num):
    sum = 0
    for n in num:
        sum = sum + n
    return sum

print(multi_add(2, 5))
print(multi_add(1, 3, 5, 7, 9))