Returning Values

So far we've mainly been discussing functions which perform some internal process, print the result, and then end. However, many of the functions we use regularly in Python don't print anything, so how do we get values out of them?

len is a good example. We provide len some argument, and then len spits out a value. We can even assign len to a variable so that we can use the value later on.

The answer is that we use a return statement.

What does a return statement do?

A return statement actually does two things.

• It ends the execution of the function.
• It returns some value.

By default, the return statement returns the value None, but we can override this default to return some other information.

tip

Even if we don't use a return statement, all functions return something.

Remember that the default return value is None, so the add function we defined earlier in this chapter actually returns None, despite not using an explicit return statement.

Using a return statement

Let's modify our add function to use an explicit return statement.

Adding a return statement is as simple as writing return at the end of the function body.

def add(x, y):
    result = x + y
    print(result)

    return  # returns None

This isn't a very useful return statement, however. Our function already ended its execution at this point, as there was no more code to run, and we haven't provided a return value, so add still just returns None.

Let's replace the print function inside add with a more useful return statement. Return values are simply placed after the return statement.

def add(x, y):
    result = x + y
    return result

So what happens when we call add now? Well, the function runs as normal, and then add returns the value of result. However, we're not printing anything anymore.

This sort of structure allows us to do several other things though. We can assign the result of calling add to a variable:

add_result = add(2, 3)  # 5

We can also pass the result of calling add into print as an argument.

print(add(1, 6))  # 7

Cool stuff! You can try it out on this editor below:

Using multiple return statements

Earlier I said that adding a return statement was as simple as writing return at the end of the function body, but you can actually put return anywhere in your function.

One thing to keep in mind is that if you put a return statement before some other code in your function body, the function will end before that other code ever runs.

For example, in the following example, we never get to assign x + y to the variable result.

def add(x, y):
    return
    result = x + y

This kind of defeats the point of the add function. However, there are cases when we might want to exit a function early based on some condition.

A few chapters back, we discussed if statements and using conditionals. You can place return statements inside a conditional block when they're used inside a function.

For example, we might want to do something like this:

def divide(x, y):
    if y == 0:
        return "You tried to divide by zero!"
    else:
        return x / y

When a user tries to divide by zero, instead of attempting the division, we just return a message, informing them of their mistake.

print(divide(10, 2))  # 5
print(divide(6, 0))  # You tried to divide by zero!