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We can now use variables
with different data types.

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But what if you want, for example, to
keep a collection of 100 temperatures?

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Are you going to create
100 variables named

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"temperature1", "temperature2",
"temperature3", etc?

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Well, this would be very
impractical, super long to

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create and prone to a lot
of errors and headaches.

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So instead, you are going to use lists.
A list is simply a collection of data.

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Or in other words, a collection of
variables which are related to each other.

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So let's create a list so you
can see what I'm talking about.

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So let's name it, we want temperature
list, so let's name it "temperature".

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List. Okay, make the name meaningful.

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Don't try to make it too complicated, okay?

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Aim for simplicity. You
want a list of temperatures,

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this is going to be
called "temperature list".

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Then you are going to
open and close brackets.

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And you are going to put the
values you want inside this list.

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So for example, I'm
going to put 12.3, okay?

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23.0, and then let's put a
negative number also, minus 12.8.

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And then another
negative number, minus 5.9.

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So here I have a list,
I'm going to press enter.

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I have a list of four
different float numbers.

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If I just do "temperature
list", I can see the list.

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So the list is evaluated here
and printed on the Python shell.

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Now what if I want to retrieve
a specific element of the list?

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In this case, I'm going
to use "temperature list"

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and also using directly brackets
here and put the index of the element.

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Let's start with one.

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Okay, you can see
actually with one, what I get

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is not the first element,
but the second element.

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Why is that? Because in programming,
usually we start to count at zero.

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So you can use the up arrow key to come
back to the different instructions you have.

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Okay, so you don't need to
write "temperature list" again.

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And then I'm going to put zero instead.

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And zero gives me, you
can see the first index here.

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So this will be zero, one, two, and three.

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So let's get each element.

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So we have zero, we have one,
let's get two, which is the third element.

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And let's get three, which
is the last element of the list.

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Now, let's say I put four.

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What is going to happen is that I have
an error, a list index out of range error.

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Okay, so that's the common
error is that you have a list

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and you try to access an
element which is outside of the list.

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Okay, so just remember
when you have a list,

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the first element starts at zero for
the index and then one, two, three, etc.

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A nice function you can use to actually get
the length of a list is simply the "len",

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so L-E-N function, which is a
built-in function inside Python.

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So you just put "len",
you open the parentheses,

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and you can put
the temperature list.

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You can put the name of the list, close
the parentheses, and then you get four.

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So this gives you the
number of elements in the list.

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You can see one, two, three, four.

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And so this information is very useful
because you can see that the last index,

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okay, here is three,
okay, zero, one, two, three.

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So the last index will simply
be the length minus one.

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And this can help you avoid getting
the index error in your program.

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Okay, so now we have seen
how to get elements from the list.

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Now how you can modify an element.

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When you simply do
"temperature list", you also put, so

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let's say zero, I'm going
to modify the first element.

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So the same as for getting the
element, but then you write equal,

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and then you can change
the value, let's say 2.4.

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So now if I try to get the
value, you can see this is 2.4.

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And if I print the list,
the first value is now 2.4.

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What you can also
do is, if you want to add

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another element here
at the end of the list,

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okay, add a new element, you
can simply do "temperature",

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so write the name of
the list, "temperature list".

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And then use the append function
like this, "temperature list.append".

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And let's say I'm going to add 10.7.

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So this is going to add a new element.

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Now I go back to "temperature list".

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And you can see I have five elements, okay.

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And the last one is 10.7.

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If I do "len" with "temperature
list", now I have five.

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So now I will be able to
actually, if I do "temperature

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list" 4, like this, I will not
get an error like here, okay.

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I will get the last element
because the length of the list is 5.

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Okay, so that's pretty much it about lists,

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and we are going to
continue to use them later on.

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So here you have created
a list with float numbers.

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But now that you can create
a list with integer numbers,

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you can also create a list containing
booleans, and also a list containing strings.

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And one recommendation
I'm going to give you is to use,

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to stick to the same data
type for all elements of a list.

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Okay, if you mix, let's say
you use integer and booleans,

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inside the same list, well, you are
probably going to have errors in the future.

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And also this can kind
of break the logic, okay.

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If you want a list of numbers,

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you are not going to put a
string inside the list of numbers.

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So stick to one data type for one list.