def a(x, y): print("I am from function a") return x(y) def b(z): # z() run the function outside def b(z) on line 13 print("I am from function b") def d(): print("I am from inner function d") z() #run the function on line 13 def c(): #register the address of function c with the content below. Function c is not run until function c is called outside on line 9. print("I am from function c") return c, d #return only 1 value out as a tuple (c, d) def d(): print("I am from function d") a(b,d)[1]() #(c, d)[1]() a(b,d)[0]() #(c, d)[0]()