Functions

As we mentioned in a previous lesson, it’s not a good idea to repeat code. If we have to write the same thing twice, chances are we’ll need to write it three times or more. This is where the notion of a function comes in. A function is a piece of code that we write once and can reuse multiple times

name = "Cortez"
age = 60

i = 0
for i in range(0, 11):
    print(f"My name is {name} and my age is {age}")

Output:

My name is Cortez and my age is 60
My name is Cortez and my age is 60
My name is Cortez and my age is 60
My name is Cortez and my age is 60
My name is Cortez and my age is 60
My name is Cortez and my age is 60
My name is Cortez and my age is 60
My name is Cortez and my age is 60
My name is Cortez and my age is 60
My name is Cortez and my age is 60

What happens if we want to display the same thing but with Tommy Vercetti and age 42? Of course, we can change the variable values

name = "Tommy Vercetti"
age = 42

i = 0
for i in range(0, 11):
    print(f"My name is {name} and my age is {age}")

Output:

My name is Tommy Vercetti and my age is 42
My name is Tommy Vercetti and my age is 42
My name is Tommy Vercetti and my age is 42
My name is Tommy Vercetti and my age is 42
My name is Tommy Vercetti and my age is 42
My name is Tommy Vercetti and my age is 42
My name is Tommy Vercetti and my age is 42
My name is Tommy Vercetti and my age is 42
My name is Tommy Vercetti and my age is 42
My name is Tommy Vercetti and my age is 42

and that’s fine

However, if we want to use this piece of code later in the program with different values for name and age, we would always have to copy and paste this for loop

It turns out that the best way, and the one that makes the code most readable, is to use a function

def my_function(name, age):
    i = 0
    for i in range(0, 11):
        print(f"My name is {name} and my age is {age}")

my_function("Cortez", 60)
my_function("Tommy Vercetti", 42)
my_function("Lance Vance Dance", 35)

We can see how our code is much cleaner and easier to read. What we did was reuse the function called my_function and call it with different values. We wrote the function once and can run it as many times as we want with different values

The word def defines a function in Python

my_function is the name of the function, meaning the name we use to call this function

Just like print(), we use parentheses ()

Inside the parentheses, we write whatever we want to name the parameters. In this case, name and age

Remember that the parameter names can be anything. The code below works as well

def my_function(n, a):
    i = 0
    for i in range(0, 11):
        print(f"My name is {n} and my age is {a}")

my_function("Cortez", 60)
my_function("Tommy Vercetti", 42)
my_function("Lance Vance Dance", 35)

After naming a function, we must put a :

Another example of a function could be

def f(name, status):
    if(status == True):
        print(f"{name} is online")
    else:
        print(f"{name} is offline")

name = "Admin"
is_online = True
f(name, is_online) # prints Admin is online

is_online = False
f(name, is_online) # prints admin is offline

Mission: Onboard Calculator

The station needs an onboard calculator. Write a function calculator(a, b, operator) that takes two numbers and an operator (+, -, *, /) and prints the operation with its result. If the operator is not one of the four, print Invalid operator.

Then read from input, one per line, the two numbers a and b and the operator, and call the function with them.

Examples

If the user types

14
12
+

the program prints

14 + 12 = 26

More examples: for 20, 8, - it prints 20 - 8 = 12; for 6, 7, * it prints 6 * 7 = 42; for 20, 4, / it prints 20 / 4 = 5.0; for 5, 2, % it prints Invalid operator.