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10.20. Pure Functions

A pure function does not produce side effects. It communicates with the calling program only through parameters (which it does not modify) and a return value. Here is the doubleStuff function from the previous section written as a pure function. To use the pure function version of double_stuff to modify things, you would assign the return value back to things.

def doubleStuff(a_list): """ Return a new list in which contains doubles of the elements in a_list. """ new_list = [] for value in a_list: new_elem = 2 * value new_list.append(new_elem) return new_list things = [2, 5, 9] print(things) things = doubleStuff(things) print(things)

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Once again, codelens helps us to see the actual references and objects as they are passed and returned.

Activity: CodeLens 10.20.2 (ch09_mod3)

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