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In this video, we'll have a
look at the update method.

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It's used to update one dictionary
with the contents of another,

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and works pretty much how you'd expect.
But you have to remember that dictionary

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keys are unique. The same key can't
appear more than once in a dictionary.

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So with that in mind, the behaviour
of update makes perfect sense.

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So let's see an example. I'll create a new
dictionary, and we'll use that to update d.

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Alright, so I'm going to leave
a comment here, this old code,

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the earlier code, and then we'll add the new code

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Alright, so I'm going to
comment the rest of this out,

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and up here, on line 16, we're
going to create a new dictionary.

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So d2 is equal to left right curly braces 7 colon

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lucky seven double quotes comma ten colon ten
in double quotes comma and 3 colon double quotes

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this is the new three, double quotes comma,
then we've got our ending right curly brace.

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Now I've deliberately mixed up
the ordering of this dictionary,

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to check the effect on the existing
keys in the dictionary being updated.

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Alright, so let's update our original
dictionary d, this one up here, on line 1.

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So I'm going to type d dot
update d2 in parentheses.

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Then we'll add some more code here, for key
comma value in d dot items parentheses colon.

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We'll print out the key in
value key value in parenthesis.

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Let's run this, to check out the results.
Put in that format, so it's a bit easier to read.

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Alright, so there's the output.
So what we've done here, is we've updated the

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values for two keys, and inserted one new value.
So the value for key 3 has been changed,

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but notice that 3 is still in the same place
- it's the fourth item in the dictionary.

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Updating the value doesn't
change the position of the key.

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That's the same behaviour we got when we
changed the value of virago in our vehicles

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dictionary, in the previous video.
We can see the same thing for 7;

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the value's changed to lucky seven, but
the key remains in its original position.

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Updating the value of a key doesn't
affect its position in the dictionary.

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Once again, that's what the documentation
means by the insertion order being preserved.

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We also added a new key, 10, to the dictionary,
and we can see that got inserted at the end.

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The documentation mentions that we
can pass a dictionary to update,

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which is what we've just done.

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It also mentions passing an iterable
of key value pairs, as tuples.

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We know of a way to create an
iterable of key value pairs as tuples.

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The enumerate function does that,
so let's have a go at doing that.

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So down here

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line 26, I'm just going to do an empty print
here, so print parentheses. Move things up a bit.

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Then I'm going to type d dot update, and in
parentheses, enumerate parentheses pantry

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underscore items and closing right parentheses.
Then we'll do the same thing, for key comma value

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in d dot items again parentheses colon,
and we'll print out key comma value again.

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Let's run the program again, and we're
looking at that second block of output.

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The first five items have
been replaced with the values

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from our pantry underscore items list.
Okay, so that's the update method.

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It takes the key value pairs that we passed
to it, and uses them to update a dictionary.

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Any existing keys have their values
replaced by the values we passed to update.

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Before we move on, I'll quickly mention
another way to update a dictionary.

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Switching back to the documentation, and scrolling
down to the update method, just down here.

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So just below the update method there's two
new operators, that were added to python 3.9.

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These are the union operator, the
pipe character you can see there,

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and the augmented union assignment operator.
That's the pipe character and the equal sign.

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If you check the description of the update method,
I'll just go up a little bit so you can see it,

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and if we compare that to the augmented union
assignment operator, you'll see that they're

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actually doing the same thing. Just go up a
little bit more, so we can hopefully see both.

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So there's the update again. Update the
dictionary with the key value pairs from other,

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overriding existing keys. You can see we've
got essentially the same thing in the augmented

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union assignment operator. So here you
can clearly see the descriptions are

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written slightly differently, but both update
a dictionary with keys and values from other.

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As you can see. The update function will also
accept keyword arguments which is, something you

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can do with a function but not with an operator.
So I suggest you stick to using the update method,

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and ignore this augmented union assignment.
So that's that d pipe equals other,

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just below the middle of the screen.
If you use either of these new operators,

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your code won't run on Python
versions before Python 3.9.

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So let's have a quick look at how long
those earlier versions will be used for.

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I've got a page here, which I want to go to. This
page has the release dates and end of life dates,

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in a table, which can be really useful to actually
know if you're using a specific version of Python.

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As you can see, Python 3.8 doesn't reach end
of life until October 2024. If you write code

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that uses these new assignment operators,
over here, your code would be unavailable

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to a lot of Python users, for at least four
years from the date I've recorded this video.

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Ultimately, it's your choice, of course, but we
certainly won't be using them in this course.

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Alright, so moving on, in the next
video we'll look at the values method

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and see how it can be useful.

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See you in the next video.