Returning Functions From Functions

Python Decorators 101 Christopher Bailey 03:23

This lesson covers how to return functions from functions. The code example in the lesson uses a function called parent() that contains two inner functions that return a string of text:

Python
      
    
def parent(num):
    def first_child():
        return "Hi, I am Emma"

    def second_child():
        return "Call me Liam"

    if num == 1:
        return first_child
    else:
        return second_child

You’ll see how to access these inner functions and assign them to variables.

00:00 If functions can be defined inside of other functions, can a function also be returned from a function? Sure. It’s time for another example. Continuing in this idea of functions inside of functions, let me have you make a new one. This one will be named parent() also, so start off with def parent(). This time you’ll have an argument of num—it will be used for selecting the child. Right away in the statement, you’re going to start with defining a new function named first_child() that doesn’t take any arguments, and for its statement, you’ll have it return a string of text that says "Hi, I am Emma".

00:41 Then, define a second_child() function. For that function, I’ll have you return text that says "Call me Liam". And last, before we return out of our main statement, returning from the function itself, we’ll set up a little condition.

00:56 If the argument num is equal to 1, return the function first_child—not calling it, but simply returning the function itself. else—in all other cases—return the other child, second_child. Again, not calling it, just simply returning it as a function. And close the statement.

01:15 So in this case, if you select parent, you’ll see that it’s a function. If you try to access first_child, it says that it’s not defined. Same with second_child.

01:29 But try this instead. Let’s set up a variable and let’s call it first. Into first, I’ll have you copy parent() with the number 1 in it.

01:40 So it’s calling the parent() function with the argument of 1.

01:45 That means if num is set to 1, it should return first_child. Okay. It looks like nothing happened. Well, let’s try a second one. Let’s set up another variable, second, and pass the argument of 2. So, what are these? We’ll look at first by itself—not call it, just type in the name and Return.

02:08 It says here that first is a function that lives inside the local scope of parent. Its name is first_child.

02:19 And then its memory location. What about second? second is a function. It lives inside parent, and second_child again is what it’s referencing inside of it. Can you call them?

02:35 Sure! If you call first() as a function. It prints out 'Hi, I am Emma'—well, it returns the string 'Hi, I am Emma'. And second()—very similar. It returns the string 'Call me Liam'.

02:50 So these two variables first and second are actual functions that are referencing—from the parent() function, inside of the scope of the parent()—the first_child function or the second_child function.

03:03 It’s referencing them.

03:08 And then they’re callable on the outside. Pretty neat! You’ve returned functions from within a function.

03:18 All right. I think you’re ready to talk about decorators, but first, let’s do a short review.

Anonymous on March 20, 2019

Nice and clear explainations though the pace for me is a little faster than I would like.

Rynaldo I Bama on March 24, 2019

It explains the concepts clearly and concisely.

snjy1609 on Oct. 27, 2022

def parent(num):
    def first_child():
        print("hi! from first_child")
    def second_child():
        print("hi! from second_child")``
    if num == 1:
        return first_child
    else:
        return second_child
first=parent(1)
print(first())

Hi All can someone please help me to understand if we call the first reference function why it also print None after printing “hi! from first_child”?

Geir Arne Hjelle RP Team on Oct. 27, 2022

Hi Sanjay.

In your example first ends up being the inner first_child function. So doing first() is the same as doing first_child() would have been if you defined first_child as a regular function (not an inner function).

When you call first() that triggers the print() within the function itself. When you do print(first()), you’re first calling first() which does its print(). Afterwards, you print the return value of first. Since first_child doesn’t have an explicit return statement, it returns None (see realpython.com/python-return-statement/#implicit-return-statements).

This behavior is not really related to the inner function. You can see the same thing in a simplified version of your example:

def first():
    print("Hi from first")

print(first())

I hope this helps you explore this further!

snjy1609 on Oct. 27, 2022

Thank you all I understood the reason of printing None.as child function is not returning anything, Hence print function is printing None.

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