Lesson 04-02: Passing Data to Functions

Accepting Function Arguments¶

Our previous functions weren’t very useful, and rightly so - all it was doing was repeating code or printing something static (unchanging). In this lesson, we will learn how to pass data to a function.

Arguments are data that is passed to a function. To allow a function to accept arguments, we have to include it in the function definition (header). An example:

def say_hello(name):
    print("Hello {}!".format(name))

The arguments in the function arguments are variable names. These variables are declared as part of the function header, and are basically telling the function to expect some data to be sent. You can have more than one argument too - they would just be separated by variables.

def add(a,b,c):
    sum = a + b + c
    print("The sum of {}, {}, and {}, is {}!".format(a,b,c,sum))

The above function takes three pieces of data and saves it in the variables a, b, and c respectively. So how do we actually send data to a function that’s ready to accept data?

Passing Function Arguments¶

When we call upon a function that has arguments, we have to supply the same number of arguments. Let’s take a look at a few examples from above:

Notice that I call this function twice - one just by passing a string (“Bob”) and another by passing a variable (other_name) that represents a string (“Hannah”). Both ways work, for now.

Note that the ordering of the arguments matter. When I run add(x,y,z) it prints out the numbers in the order of 1, 2, and 3. However, when I run add(z,y,x), it prints out the numbers in the order of 3, 2, and 1.

What Actually Gets Passed?¶

Although it might seem like we are passing variables, it’s very important to remember that we are just passing the value within a variable. The variable itself will not be changed. Let’s look at this example:

In this code, we are sending (the value of) x to the function add_one, which stores it in a variable a and increases is by one. We can see that a was increased by 1 because of the output. However, the value of x is not changed.

Checks For Understanding¶

Q#1¶

In the space below, write a function called times_10 that takes in a single number argument and prints the value of the number times ten (you can assume that the data passed to the function will be a number). Do not change any of the function calls. If done correctly, you should see the following as output:

30
500
15.0

Q#2¶

In the space below, write a function called compare that takes two number arguments and prints the value of the higher one. You can assume that the data passed to the function will be numbers. Do not change any of the function calls. If done correctly, you should see the following as output:

5
100
10.001

Q#3¶

In the space below, write a function called compare3 that takes three number arguments and prints out the highest one. You can assume that the data passed to the function will be numbers. Do not change any of the function calls. If done correctly, you should see the following as output:

3
10
-6

As a hint, given a, b, and c, you would know that a is the highest number if a is greater than both b and c.

Lesson 04-02: Passing Data to Functions¶