Continued adventures in learning Python (started here):

A function gives you a return value based on an argument that you input.  The function len will give you a return value of the number of elements in an object.  The argument you provide is the name of the object.  In this example the object is called “names.”

You create a function by using the syntax def (define).  This function is called “Mary” (it could be called anything).  The function doubles the argument.