What is the use of a return statement?

Question

Let me clarify; Let us say that you have 2 functions in Python:

def helloNot():
    a = print("Heya!")
helloNot()

Which will print out Heya! without a return statement.

But if we use a return statement in this function:

def hello():
    a = print("Heya!")
    return a
hello()

This will print out Heya! as well.

I have read and learned that a return statement returns the result back to the function but

• doesn't the result get automatically returned by whatever result you have without a return statement inside a function?

In our case let's use the function helloNot() (our function without the return statement):

our variable a, which is a print statement returns the result to the function when we call it or am I missing something?

On a side note,

• Why and when would we use return statements?

• Is it a good habit to start using return statements?

• Are there a lot more advantages to using return statements than there are disadvantages?

EDIT:

using the print statement was an example to better present my question. My question does NOT revolve around the print statement. Thank you.

Answer 1

Normally, when you call a function, you want to get some result. For example, when I write s = sorted([3,2,1]), that call to sorted returns [1,2,3]. If it didn't, there wouldn't be any reason for me to ever call it.

A return statement is the way a function provides that result. There's no other way to do that, so it's not a matter of style; if your function has a useful result, you need a return statement.

---

In some cases, you're only calling a function for its side-effects, and there is no useful result. That's the case with print.

In Python, a function always has to have a value, even if there's nothing useful, but None is a general-purpose "no useful value" value, and leaving off a return statement means you automatically return None.

So, if your function has nothing useful to return, leave off a return statement. You could explicitly return None, but don't do that—use that when you want the reader to know you're specifically returning None as a useful value (e.g., if your function returns None on Tuesday, 3 on Friday, and 'Hello' every other day, it should use return None on Tuesdays, not nothing). When you're writing a "procedure", a function that's called only for side-effects and has no value, just don't return.

---

Now, let's look at your two examples:

def helloNot():
    a = print("Heya!")

This prints out Heya!, and assigns the return value of print to a local variable, which you never use, then falls off the end of the function and implicitly returns None.

def hello():
    a = print("Heya!")
    return a

This prints out Heya!, and assigns the return value of print to a local variable, and then returns that local variable.

As it happens, print always returns None, so either way, you happen to be returning None. hello is probably a little clearer: it tells the reader that we're returning the (possibly useless) return value of print.

But a better way to write this function is:

def hi():
    print("Heya!")

After all, we know that print never has anything useful to return. Even if you didn't know that, you know that you didn't have a use for whatever it might return. So, why store it, and why return it?

Answer 2

You should use return statements if you want to compute a value from a function and give it back to the caller.

For your example, if the goal of the function is just to print a fixed string, there's no good reason to return the return value of print.

Answer 3

If you don't return anything from a function, Python implicitly returns a None. print falls in this category.

In [804]: a = print('something')
something

In [806]: print(a)
None

Similarly with functions that the user defines

In [807]: def f():
     ...:     print('this is f')
     ...:

In [808]: fa = f()                # Note this is assigning the *return value* of f()
this is f

In [809]: print(fa)
None

Answer 4

What you are doing does not require a return statement, you're right but consider you want to calculate an average.

def calculateAverage(x, y, z):
    avg = ((x + y + z)/3)
    return avg

Now that you have declared a function that has the ability to take 3 variables and return the calculated average you can now call it from any function and not have to have bulky code.

a = calculateAverage(7, 5, 9)
print("Average is:" + a)

Which will print to screen "Average is: 7"

The power of functions and return values is that you are able to make your code more readable by means of placing a single call to a sophisticated function in your main logic, which means you now have less lines of code and it is more legible/maintainable in the longrun.

Hopefully this helps.