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- [Instructor] In this
video, we're going to discuss

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the dictionary method's keys and values.

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And I'm also going to talk
in a little bit more detail

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about the items method as well.

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Now for demonstration purposes,

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we'll use this months dictionary,

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which contains three key
value pairs, once again,

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and let's start out within a for loop here

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in which we demonstrate the keys method.

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Now, the items method that
we looked at previously

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gave us back each key
value pair as a tuple,

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the keys method simply grabs each key

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from the dictionary and gives us back

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something that's iterable that I can then

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walk through and in this case I'll just

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display the month name
followed by a couple of spaces.

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So let's go ahead and do that.

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Now, as you can see
here, the keys came out

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in the same order that they were inserted

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into the dictionary once again,

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and that still is going to depend on

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what version of Python you're using.

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Now, if you installed Python
three dot seven and higher,

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as I specified back in the
before you begin lesson,

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then you'll wind up...
you should wind up with

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the same order that I'm seeing here,

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however, if you're using an
earlier version of Python,

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the order in which these come out

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may be different on
your particular machine.

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Now, let's also go ahead and
demonstrate the values method.

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As you would expect, it's going
to give you back the values.

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Notice that the values
for the corresponding keys

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came out in the same order as again,

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they were defined in
the original dictionary.

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Now, I said when we first introduced

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the items method, that it was returning

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an iterator that allowed
us to iterate through

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in our case, the items previously,

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and now, the keys and the values.

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But in all three of these methods' cases,

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what's really being returned is

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what's known as a dictionary view.

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A dictionary view is effectively a window

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into the dictionary so you're looking at

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that dictionary's data, and
if you modify the dictionary

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after you acquire the view,
the next time you iterate

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through the view, you'll
see the modified contents.

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So let me demonstrate what
I'm talking about here.

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Up above, we iterated immediately through

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whatever keys returned, but let's say

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we store that into a variable.

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So now we have this object which is a view

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into the months dictionary.

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And let's iterate through that,

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because we wanna just prove that we can.

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So... whoops, sorry about that.

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So if I go ahead and execute that,

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you see that indeed,
January, February, and March

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are displayed as they were up above.

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The only difference between snippet two

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versus snippets four and five is that

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I took the intermediate
step of creating the

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variable months view.

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So now, if we go modify
the months dictionary,

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let's say we go and
say months sub December

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and we give it the value 12, now of course

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the months dictionary has been modified

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and we can see the updated dictionary

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with four key value pairs.

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So at this point of
course, if we were to get

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months dot keys or months dot values

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and iterate through them
like we did up above,

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we would expect to see
four items get displayed

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in each case.

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But what about when I iterate through

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months underscore view, which was acquired

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when the months dictionary
only had three keys in it?

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Well, let's see what happens.

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So, for each of those keys,
we're going to display them.

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So for each key in the months view,

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display the key followed
by a couple of spaces.

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And when I go ahead and do that,

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notice that, indeed, we get
four items being output,

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even though we're iterating
through the months view,

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which was created back
up here in snippet four

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when we still only had three keys,

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so this helps prove that in fact

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the view is looking at the
original dictionary's data,

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it doesn't maintain its
own copy of that data.

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Okay, so now that we've
seen the keys, values

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and items methods and talked a little bit

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about dictionary views,
sometimes you'll want to

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acquire either the keys,
the values, or the full

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item tuples to place them
into a list for example.

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So in Python it's real simple
to do things like that,

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I have the built-in list function

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and I can say months dot keys

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and it will simply walk through those keys

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and insert them into the list

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and return the new list object.

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I can of course easily do
the same thing with values,

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and if you're curious, we can also do

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the same thing with items in which case,

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we see the actual tuple objects

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that have been placed into the list

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that was being created in snippet 11 here.

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So this just further proves
that the items method

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really does give us access
to tuples of key value pairs.

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So at this point, let's just take a look

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at one other thing that you may find handy

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once in a while.

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Sometimes it's useful to iterate

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through a dictionary's
keys in sorted order.

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So in the case of our
keys, these are strings,

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so sorted order would basically mean

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listing these alphabetically,

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remember, however, that when
you compare strings in Python,

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it's based on the
underlying numeric values

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of the characters, so it's really a

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lexicographical comparison.

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Now in this case, each of the four keys

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starts with a capital first letter,

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so based on that, we would expect

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that these will be sorted alphabetically

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if we iterate through them in that order.

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So let me go ahead and copy one additional

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loop here and paste it in.

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In this case, we're
going to take the result

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of the keys method and hand it off

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to that built-in function sorted

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that we demonstrated with
lists in the preceding lesson.

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So it's going to acquire the keys,

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give me back an iterator that walks

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through those keys in sorted order,

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whatever sorted order means for the keys,

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in this case lexicographical order

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because they're strings, and
for each of those month names,

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we want to display them and in fact,

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we get alphabetically now December,

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February, January, and March.

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Now you may not want to
walk through month names

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in that order, but you
might be, for example,

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keeping track of word
counts in a body of text

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and what you might want
to do is order the words

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alphabetically so that you can then

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see by word easily what each count was.

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Or maybe you want to order
them not alphabetically

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but by the values of those keys,

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which would be the counts of the keys,

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and there's lots of things like that

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that you'll encounter as you start

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working with larger bodies of
data stored in dictionaries.