def add(x, y): return x + y def do_twice(func, x, y): return func(func(x, y), func(x, y)) a = 5 b = 10 print(do_twice(add, a, b)) Please explain step by step Which is caller here? Explain the 3rd and 4th line ? why in 4th line we write add(add(x,y),add(x,y)) which is function of 1st line ? how can we write function after return statement insted of (x+y+x+y )=30?

Answer 1

we first call the function do_twice and we pass 3 variables - add (the add function), a (having the value of 5), b (having the value of 10)

3rd line defines a function do_twice accepting 3 arguments (func, x, y)
since we called the function, those arguments would have the values we passed on to it.
the 4th line - will then become add(add(x,y), add(x,y))

we will then first evaluate the 2 inner function calls add(x,y) -> add(5,10) which will evaluate to the value of 15.
so now that we have evaluated the inner function calls' values we now have the outer function call which now looks like - add(15, 15)
so evaluating that we get 30.

as for your last question I don't quite understand it.

Answer 2

def shout(word):
return word + "!"
speak = shout
output = speak("shout")
print(output)