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Alright so continuing with our code. So
far we've tested this code with an item

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that does exist in the list. Let's now
see what happens if that item doesn't exist.

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So what I'm going to do is change line three.

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Instead of searching for spam,
I'm going to search for albatross.

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Alright, we're gonna run the program now,
and you can see item found at position None.

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Now that message is a bit misleading - the item
wasn't found at all - but you can see that

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None is coming from line four in our
code. We initialized found_at to None

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on that line. Because albatross wasn't
found, line nine of our code wasn't

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executed and found_at wasn't 
given another value. It's very important

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that we bound found_at to
something on line four. So let's see what

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would have happened if we hadn't have
done that. I'm gonna comment out line four.

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We'll run the program again. This time
you can see we've got an error, and the error,

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right over at the right hand side
there, line 12. And on line 12 we're

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trying to print the value of found_at
but it hasn't been given a value,

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and in fact my IDE has highlighted
found_at on line 12,

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if we hover over it, name found_at
can be not defined. So that's an error.

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Now the code would work if albatross was
found, because found_at would

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have been attached to a value on line 9.
I'd better uncomment that line to fix that error.

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So that explains why we had to
initialize found_at,

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but what's this None that I initialized it
to? Well None is a constant that

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represents nothing. found_at
now exists but it doesn't yet have a

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value when the code on line 4 is
executed. One thing we can use it for

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here, is to improve the message we get.
Let's have a go at doing that, and we can

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change the code. So on line 12, what I'm
going to do is add some code there:

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if found_at is not None :
then we'll indent the next line.

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Then we'll put an else to the left-hand
margin print parentheses double quotes

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left and right curly braces
not found, and our double quote dot

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format parentheses item_to_find.
And now that we've done that,

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we run the program,
we get a better message when an item is

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not found, as you can see here. So looking
at the code, we've initialized found_at

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to None on line four. If
it's still None when we get to line 12,

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then we didn't find the item we're
looking for. Alright I want to finish

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this video now with an apology.
We shouldn't write code like that for loop,

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on lines seven through ten. Python
is an incredibly rich language and one

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of the reasons that it's so successful,
is because it comes with so much

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included as standard. We've only looked
at a small part of the language so far,

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and the examples I use have to reflect
that. Even then, I've had to introduce the

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list type for this example. The code
demonstrated how to use break and why

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you'd want to, but there's a much easier
way to write this code. So what I'm going

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to do, so I'm going to comment out the
for loop

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if item_to_find is
in shopping_list colon

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found_at is equal to shopping_list.index.
Then in parentheses,

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item_to_find, then we've
got a closing parenthesis there.

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Run the program now, and you see we've got the
same result there. And just to confirm that it

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is working, if I change albatross back
now to spam, which it originally was at

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the start of the video. Run this, item
found at position three. So that also works.

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00:04:05,880 --> 00:04:09,580
As I said, Python is a very
rich language. It's got all sorts of

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things included and we'll be seeing most
of them in this course, and you'll learn

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what line thirteen is doing in the next
section of this course. I'll also explain

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why lines twelve and thirteen aren't
very efficient and how we can improve

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that code. Before that though, in the next
video, we'll look at another type of loop -

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the while loop.
See you in the next video.