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Alright so let's talk about the break
statement in Python. So it's also

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possible to break out of a for loop
completely, using the break statement.

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If we replace continue with break, we won't get
a reminder to buy bread or rice because

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the loop will terminate when it gets to
spam. So what I'm going to do is delete

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this commented code out completely from
the previous video and then we're going

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to change continue to break.
Firstly, lets run it,

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and you can see what happened there.

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Basically, we saw the output milk pasta

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and eggs, but after we executed break we
didn't get a reminder to buy bread or

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rice, and that's because the loop
terminated when it got to the break

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statement on line five, when it got to
spam. So break can be very useful.

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Imagine we're searching through a list
containing thousands of items. If we find

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the item we're looking for,
there's no point looking through the

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rest of the list. You generally stop
looking when you find what you've looked for.

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So what I'm going to do now is copy the
first line, line one here,

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and we're going to create a new file called searching.

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Ok, I've pasted that line back in.

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Alright, so let's use a for loop to search for an
item. We're going to start with a couple

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of variables, so on line three I'm going to
type item_to_find

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equals spam in double quotes, and on the
next line found_at is equal

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to None, noting that it starts with a capital N.

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So we're gonna search for spam and I've
bound the variable item defined in the

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string value that we're looking for,
that's on line three. If we find it, we

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want to know its position in the list.
We're going to store that in the

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variable found at, or found_at.
Now initialize that to None on line four,

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and None is a constant that's used to
show that something doesn't have a value,

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so it's roughly equivalent to null
in C or Java. Now I'm going to come back

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to that line because new programmers
might be wondering why we've attached a

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variable to something that doesn't have
a value. It doesn't seem like a very

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useful thing to do. Well it actually is
useful. I wouldn't

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be doing it otherwise, but it'll be easier
to show why it's useful when we see our

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code working. Alright so now what we
need to do is write our for loop.

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I'm going to write this one slightly
differently. What we're going to do is

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loop over the index positions of the
list instead of looping over the items.

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So to do that, on line six I'm going to
type for index in range

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left parenthesis len left parenthesis again,
shopping_list and then we've

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got the two right parentheses and a
colon. On line seven, if shopping_list

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then in square brackets,
index and then closing right square

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bracket. That's equal to two equal signs
item_to_find :

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found_at is equal to index. Okay so
there's our code. So I've used a new

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function there - the len function.
Len is short for length and lets us know

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how many items are in the sequence. Our
shopping list contains six items, so len

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left parenthesis shopping_list
right indices on line six,

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that's going to return the value six. So that
means index, therefore, will get the

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values 0 1 2 3 4 and 5. Remember that the
last value in the range isn't included.

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So indexing a list is exactly the same
as indexing a string, and we covered

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that in the last section. The item at
index position 0 is milk, the item at

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position 1 is pasta, eggs is at
position 2 and so on. If we find the item

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we're looking for, which is the test on
line 7, we store its position in the

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variable found_at on line
8. When the loop terminates the value of

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found_at, we'll either still be
null as we defined it originally on line 4,

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if we didn't find the item we want, or
it'll be in the index position of the

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item in the list, which was set on line
8. Alright, so the last bit of code now

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we need to add, is to print out what we found.
So let's do that. Just as a reminder here,

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I'm gonna put a comment on line 6.

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This is what effectively is happening
here, that line seven, that's the len

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shopping list returns 6, and that's why
it's equivalent to what I've typed there

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if we weren't using the len function.
Alright so on line eleven then, we're

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going to type print parentheses double
quotes Item found at position and left

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and right curly braces dot format,
and in parentheses found_at

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and then we've got our closing right parenthesis.
If you run the program,

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you can see it says Item found at
position 3, and that's correct.

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Spam is the fourth item in the list, at
index position three, and obviously as

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the count starts from zero. Now I don't
think I need to step through the for

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loop from the beginning, but do that if
you want to see, going around from the

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start. What I'm going to do is set a
breakpoint on line nine, where we assign

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the index number to our found_at
variable. If you run the code in the debugger,

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you can see index is set to the
value of three and we've found the item

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we're looking for. found_at is
currently still None. When I step over

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you can see that three has now been
assigned to found_at

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and that's good. Our program is working and
has found spam in the list. What's not so

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good is what happens next. We found what
we're looking for and there's no point

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continuing to search, but when I step
over again which I'll do now, we can see

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that the code's still searching. You'll
have to continually step over here, till

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that finishes its work. Eventually you can
see the program is now completed. So this

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is where break can be useful. What we're
going to do is add a break after line nine,

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indented to the same level, as you
can see there. So if we repeat the test

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I'm going to debug it again, found_at
currently is set to None. If I step over,

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found_at is now 3. When we're
ready to execute the break statement, a

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break causes Python to jump out of the
loop, so when I step over now, you can see

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the execution has gone straight to line
twelve. That's more efficient because we

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don't keep going around the loop after
findng the item we want. Step over one

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more time, and that's terminated the
program, as you can see.

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So that's the break statement. If you
need to jump out of a loop, that's how to

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do it. We'll be using break in some other
examples, later in the course.

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I'll stop the video here and in the next one,
we'll look at what happens when the item we

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want isn't in the list.
See you in the next video