let' take simple example if we again use the values and the mean of this data (xis so the numerator of the fraction is computed as ( ) ( ) ( ) ( ) ( ) finishing out the calculation gives us ss - the standard deviation is about you can see how the first step of this calculation uses both the mean (which can' be computed until all of the numbers have been enteredand each individual value as well computing the standard deviation this way requires some method to remember all of the individual values that were entered applying lists in order to complete our enhanced statistics programwe need way to store and manipulate an entire collection of numbers we can' just use bunch of independent variablesbecause we don' know how many numbers there will be what we need is some way of combining an entire collection of values into one object actuallywe've already done something like thisbut we haven' discussed the details take look at these interactive examplesrange( [ "this is an ex-parrot!split(['this''is''an''ex-parrot!'both of these familiar functions return collection of values denoted by the enclosing square brackets these are listsof course lists and arrays as you knowpython lists are ordered sequences of items in factthe ideas and notations that we use for manipulating lists are borrowed from the mathematical notion of sequence mathematicians sometimes give an entire sequence of items single name for instancea sequence of numbers might just be called ss sn- when they want to refer to specific values in the sequencethese values are denoted by subscripts in this examplethe first item in the sequence is denoted with the subscript