What is the purpose of the return statement?

Question

What is the simple basic explanation of what the return statement is, how to use it in Python?

And what is the difference between it and the print state

Answer 1

Think of the print statement as causing a side-effect, it makes your function write some text out to the user, but it can't be used by another function.

I'll attempt to explain this better with some examples, and a couple definitions from Wikipedia.

Here is the definition of a function from Wikipedia

A function, in mathematics, associates one quantity, the argument of the function, also known as the input, with another quantity, the value of the function, also known as the output..

Think about that for a second. What does it mean when you say the function has a value?

What it means is that you can actually substitute the value of a function with a normal value! (Assuming the two values are the same type of value)

Why would you want that you ask?

What about other functions that may accept the same type of value as an input?

def square(n):
    return n * n

def add_one(n):
    return n + 1

print square(12)

# square(12) is the same as writing 144

print add_one(square(12))
print add_one(144)
#These both have the same output

There is a fancy mathematical term for functions that only depend on their inputs to produce their outputs: Referential Transparency. Again, a definition from Wikipedia.

Referential transparency and referential opaqueness are properties of parts of computer programs. An expression is said to be referentially transparent if it can be replaced with its value without changing the behavior of a program

It might be a bit hard to grasp what this means if you're just new to programming, but I think you will get it after some experimentation. In general though, you can do things like print in a function, and you can also have a return statement at the end.

Just remember that when you use return you are basically saying "A call to this function is the same as writing the value that gets returned"

Python will actually insert a return value for you if you decline to put in your own, it's called "None", and it's a special type that simply means nothing, or null.