Pure Functions

Given an input x to a function f the result f( x ) will NEVER produce Side Effects, or more abstractly, will not influence the outside world.

//Example of a pure function
def add(x, y):
	return x + y

//Example of a NON-pure function
def add_element_to_list(list, element):
	return list.append(element)

List changes state, because of the append function Before function call list = [1,2,3] After function call list = [1,2,3,4]

//Make it PURE
def add_element_to_list(list, element):
	return list + [element]

Before function call list = [1,2,3] After function call list = [1,2,3]