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Welcome back.

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In today's lesson,

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you're going to learn a powerful new command for sorting.

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Sorting is a big deal in the computer science curriculum.

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In a typical computer science curriculum,

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you would learn several different sorting algorithms and

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you'd analyze properties of those algorithms.

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In my first programming course back as an undergraduate,

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I had to implement something called merge sort where you take the items,

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you keep chopping them in half until you get to very

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smallest which are already sorted and it turns out

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that taking two already sorted lists and merging them together

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into an even bigger sorted list is something that you can do pretty easily.

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It goes pretty fast,

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and so we build up from these small sorted list until we have the whole thing sorted.

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I spent days and days in the computer lab.

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It was before we had personal computers.

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So, I had to go to the computing lab and every time I hit run,

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I had to wait for the mainframe to run the program and print out

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a stack of papers telling me how the program would run.

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After many hours over several days,

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I proudly took a stack back,

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back home and showed all my roommates,

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"Yeah, I finally did it."

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It won't be so hard for you.

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We are not going to look at details of sorting algorithms.

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We're just going to use a built-in Python function.

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But we do want you to have a little mental model of what happens inside of

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a sorting algorithm because it's going to help you to figure out how to invoke it well.

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We've given you these great videos from [inaudible] into university

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illustrating sorting algorithms using Hungarian folk dances.

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You'll watch a couple alternative Hungarian dances showing different sorting algorithms.

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Don't worry about the details of the algorithms,

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but do notice there's something that they have in common.

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They always involve a bunch of

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pairwise comparisons which are interactions between a pair of dancers,

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two dancers will look at each other or each wearing a number,

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and they look at their numbers,

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and they do dancing and the one with the higher number

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always ends up on the right at the end of that interaction.

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After they've done a whole bunch of these pairwise comparisons,

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the dancers are in order by their numbers.

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So again, the particular sorting algorithm is not our focus here.

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We're just going to call a function that does the

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sorting for us and whatever sequence we give it comes back sorted in the order we wanted.

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At the end of this lesson,

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you will be able to invoke the sorted function to sort any sequence.

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You'll be able to specify either low to

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high order or high to low using the reverse parameter.

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You'll be able to specify a property to sort by using a key function.

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And in a later lesson,

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you'll learn some more advanced sorting things.

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So, we'll see you at the end.