Example in Functional Programming, 1/3

Question

Hi everyone,

So, this lesson starts off by giving this example:

def apply_twice(func, arg):
return func(func(arg))

def add_five(x):
return x + 5

print(apply_twice(add_five, 10))

and that gives a result of 20.

I don't understand how 20 is the result of calling the function twice? The function add_five takes the root argument, which is 10, and adds 5 to that...so we've got 15 so far...then that function is doubled by apply_twice. So if anything, shouldn't the result be 30?

Thanks!

Answer 1

apply_twice function returns func(func(arg)) where func is add_five. So, when 10 is passed as arg, 5 gets added twice
10+5+5=20

Answer 2

It doesnt work like that.
() is for the function call. Not for multiplication 😅

Answer 3

In this example function apply_twice returns add_five(add_five(10)). That means first time function add_five takes 10 and adds 5, so you have add_five(15). After that second time function add_five takes 15 and adds 5, so finally you have 20 as output.

Answer 4

Gotcha, I understand now. So, if I hypothetically had a third function called multiply_result, it'd layer onto the existing two functions like multiply_result(add_twice(add_five(10))), right? If multiply result were just result*2, then it'd be 10+5, then +5 again for 20, then 20*2 for 40.

Answer 5

Ah okay, I was playing around with the code, trying different arguments, and I saw it was just adding 5 twice to the root argument, but I guess I didn't understand how it's not multiplied.

So, to illustrate what I mean by that, if you had 5(5(5)), that'd be 5(25) or 125. So, using that same logic, this function would look something like 2(10+5(10)), which is completely wrong.

Answer 6

good