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- [Narrator] In this video, I'd like to

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take a a look at sorting
the elements of a list

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and then showing you
another way to do sorting,

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which will work not only with lists,

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but also with the contents of a string

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or with tuples as well.

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So for the purpose of
this example to start out,

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let's create this list called numbers.

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And as you can see, I've
purposely created the list

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out of order, so that we can demonstrate

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sorting capabilities.

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Now, it turns out that
built in to the list type

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is a sort method that allows you to modify

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a list in place.

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So if I type numbers, and a dot, and tab,

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you can see all the different
methods available to you

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for the list type in Python,

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one of which is sort.

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So lets go ahead and invoke sort.

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And that's an in-place sort,
so now if I look at numbers

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after the operation,

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you can see that indeed

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it modified the list
and now the list is in

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ascending order by default.

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Now let me redefine that list once again,

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because you can also sort in
descending order by default.

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Not by default, but by passing an argument

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to the sort method.

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So if we say reverse=true, that says

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I would like to sort in descending order.

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So now if I take a look
at the values in numbers,

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I can see them top to bottom.

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Ten down to one.

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So that's in-place sorting
with the sort method

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of a list.

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Now, if you don't want to
modify the list's contents

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or if you're working with a
sequence that's immutable,

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there's also a built-in
function for Python

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called sorted.

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So let's go ahead once
again and create that list

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with the elements out of order.

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And for this one, we'll assign the values

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to a variable after the
operation that's going

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to sort those elements.

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So let's say we have a variable called

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ascending_numbers and
we're going to assign that

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sorted, with numbers as an argument.

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Now, sorted is the built-in function.

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It takes as its argument
an iterable object,

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some sort of sequence I can iterate over.

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And it gives back a list of values

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in ascending order by default.

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So if I now go and display the contents

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of ascending_numbers,

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we can see that indeed, this new variable

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contains the values in ascending order,

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but it did not modify numbers.

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And to prove that, we can evaluate numbers

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and see that indeed, it still contains

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the original values that we defined

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back in snippet seven.

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So that's sorted with a list,

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but I also mentioned the
fact that you can use sorted

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with immutable types as well.

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So let's go and create
a string called letters.

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We just have a bunch
of random letters here

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and they are clearly not
in alphabetical order.

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So let's define that.

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And we can go ahead and
use the sorted method,

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or function rather,
with letters to get the

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characters in this case
in alphabetical order.

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So let's call this ascending_letters.

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And I'm going to assign
the result to a variable

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for a moment, just to prove
to you that the original

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letters string is left unmodified.

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Now, of course a string is
imutable in the first place,

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so that should still be the case.

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So let's go ahead and
sort the letters string.

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And now if I evaluate ascending_letters,

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you can see that it gives me back a list,

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not a string.

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A list of the individual
letters in alphabetical order.

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And actually it's not
truly alphabetical order,

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it's in lexicographical order,

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where it's ordering
those characters based on

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their underlying numeric
values in the character set

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used underneath the hood,

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which is the Unicode character set.

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So here you see that we can in fact sort

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the contents of the string letters,

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but we get that back as a list

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containing the individual letters.

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And just to show you that
letters remains unchanged,

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there is the original letters string.

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Now, you can also use this with tuples.

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So let's say I have the following tuple,

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which is just the collection
of strings red, orange,

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yellow, green, blue.

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And let's create a new
variable once again.

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So we'll call this one ascending_colors

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and let's sort that.

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So hopefully now when we
evaluate ascending_colors,

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we will see those, in
this case what appears

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to be alphabetic order,

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but again, it's really
lexicographical order.

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So if I had uppercase
and lowercase letters

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in some of these strings,

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they may not appear in the same order

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that you're seeing right now.

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And separately, notice that
it gives me back a list,

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even though I started with a tuple.

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And finally, notice that
if I display colors,

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it is still a tuple with
the strings in their

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original order.

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So as you saw here,

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we were able to sort lists
in-place with the sort method

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and we were able to sort lists,
string contents, or tuples,

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with the sorted built-in function.

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The one thing I didn't demonstrate here

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is the fact that you can
also sort in descending order

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with the sorted method.

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So for example, if I say sorted,

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and let's say we want to
sort these color strings

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in descending order.

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We can give a second argument that says

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reverse=True, just like we
did with the sort method

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built in to a list,

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and we get back a list
containing those strings now

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in descending order
from highest to lowest.

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And again, because I'm
using all lowercase letters,

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they're in alphabetical
order in descending order

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in this case.