# 10.19. 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.

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

(ch09_mod3)

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