Someone please can explain me how this little tiny program works? Especially the first 2 lines of code that lead to the result.

Question

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

def add_five(x):
return x + 5

print(apply_twice(add_five, 10))

>>> 20 #To this

Answer 1

the code print the result of apply_twice function, called with the add_fivd function as first argument and 10 as second argument...

so, apply_twice receive add_five function in func argument variable and 10 in arg argument variable, and return return value of func(func(arg)) wich is equivalent to add_five(add_five(10))...

first is applied inner add_five(10) wich return 15, then outer add_five(15) wich return 20...

so apply_twice return 20, and 20 is printed ^^

Answer 2

go through everything one step at a time.

apply_twice(add_five, 10)

in apply_twice(), it takes a function and an argument as parameters.
Inside the apply_twice() function, it returns a call to the function given, with the parameters being:

func=the same function given
AND
arg=an argument for the function given

that looks like:

apply_twice(add_five, 10)
breaks down to (inside the function):
add_five(add_five(10))
which is:
add_five(15)
and finally:
20