hey CS dojo in this video I'm gonna
introduce you to list in Python the list
is a type of data just like strings and
integers that we've seen so far and it's
used to store a list of things and it's
similar to arrays in some other
languages like Java so let's take a look
at one example here to define a list you
can just write a equals open square
bracket 3 comma 10 comma minus 1 close
square bracket and this line means
define a new list with the elements 3 10
and minus 1 and assign this list to this
variable a and just a quick note here
that you can download this sample file
by going to CS no 2 dot io / Python 4
and another quick reminder that you
don't necessarily have to use Jupiter
notebook to follow this course you could
use for example per charm which is a
good IDE for Python now let's run the
cell and once we run the cell a should
be defined so let's print a with print
parentheses a and we see that we get a
list with the elements 3 10 and minus 1
what if we wanted to add an item to this
list you can do that with a dot append
parentheses 1 this means append the item
the number one to the list 8 so this dot
notation is a pretty common one and
you'll see more of that later in this
course so this function append is
basically a predefined function that you
can use on the list datatype so again
that's a dot append parentheses one
let's execute this cell and once we
print a you see that the number 1 has
been added to this list so one
interesting thing about the Python list
which is different from some other
languages like Java is that you can mix
types in a single list so you could have
a list containing numbers as well as a
string let's see how that works by
appending the string hello to the list a
with a dot a pen
parentheses double quotes hello let's
print that with print a execute this
cell and you see that this list now
contains hello the string as well as the
numbers a list could even contain
another list so let's see how that works
with ADA app in square brackets 1 comma
2 so this means create a new list with
the elements 1 & 2 and then append it to
this list let's see how that looks with
print parentheses a and let's run this
cell and now you see that we have a
bunch of numbers and then a string which
is hello and another list within the
single list okay what if you wanted to
delete an item from this list for
example the last item to delete the last
item you can do a dot pop parentheses so
we're using the dot notation again here
and pop is another function that's
predefined for the list datatype and
that's why we can just write a dot pop
open parentheses close parentheses and
to see the result you can of course
print a and let's run the cell and you
see that a now has the numbers and the
string but not the list because that's
popped or deleted
let's delete the string as well this
Hello string with a dot pop which still
is the last item of the list of course
and then let's print a and you see that
it now has numbers only now there are
many other predefined functions other
than pop and a pen on the list data type
but a pen and pop are two of the most
common ones okay what if you wanted to
retrieve a specific item from this list
for example the first item the second
item or the third item to do that you
can just write a square brackets 0 and
this means retrieve the item from the
list a with the index 0 and in Python
just like in many other languages the
index starts at 0 so the first item in a
list has the index 0 and the second item
as the next one the third item has the
index 2 and so on ok so we want to print
this item just to make sure we got the
right one but actually interpreter
notebook you don't have to use the print
statement every time you could just
write a square bracket 0 here and when
you run this cell you get the first item
in the list but to keep it consistent
and also to make sure it works in any
other platform for example Park charm
I'm gonna use the print statement every
time okay what if you wanted to retrieve
the fourth item this number one to do
that you can just do a square brackets 3
so the fourth item has the index 3 and
then let's print that and we get 1 and
what if you wanted to change the content
of this list so what if we wanted to
change this number 3 to 100 to do that
you can first select that item with a
square bracket 0 that's the first item
in the list and then you can assign a
new number or any new value to it with a
square bracket 0 equals 100 let's run
this cell and then let's print a again
with print parentheses a and you see
that the first value of this list is 100
now instead of 3 okay now I'm gonna give
you a quick exercise problem to practice
what you've learned so far let's say you
have a list with three strings inside so
you have B equals square brackets double
quotes banana comma double quotes Apple
comma and then Microsoft can you swap
the first value of this list whose index
is of course 0 with the last item of
this list before I show you my solution
to this problem I'm going to show you a
model you can use for thinking about a
list in Python when you have B equals
banana Apple Microsoft the way you can
think about it is that B is going to be
sort of like three boxes put together or
one giant box one long box
with three compartments and each of
those compartments acts like a variable
so each of those refers to a value in
this case the first compartment refers
to banana and the second element refers
to Apple and the third element of course
refers to the string Microsoft and I'm
going to show you my solution first
right temp equals B square brackets 0 so
we're defining a new variable called
temp for a temporary variable which is
going to refer to what B square bracket
0 refers to which is this one and then
you can write B square bracket 0 equals
B square brackets 2 so we're saying the
first compartment should now refer to
whatever the third compartment refers to
because like I said the index for the
first item is 0 and the index for the
second item is 1 and the index for the
third item is 2 so after this line the
first compartment or the first element
will now refer to what the third
compartment refers to which is Microsoft
and once you have that you can write B
square brackets 2 equals temp and the
third compartment now will refer to what
temp refers to which is banana as a
result after these pieces of code we
have the desired result so that's a list
with the first compartment referring to
the value Microsoft and the second
element being Apple and the third
element being banana the string ok let's
make sure that method works in code
first print the current lists with print
B and we have banana Apple and Microsoft
just like we saw will first define a
temporary variable with temp equals B
square bracket 0 and then assign the
value of B square brackets 2 to be
square brackets 0 and then assign what
temp refers to to be square brackets 2
and then at the end we're going to print
B
okay that's correct we have Microsoft
Apple banana now and actually there's a
shortcut for this and that's B square
brackets 0 comma B square brackets 2
equals B square brackets 2 comma B
square brackets 0 let's see if that
works by printing B and once we print be
the first element and the last element
should be swapped again so we should get
the same list as the first one banana
Apple and Microsoft and that's what we
get so this is definitely a valid way to
swap two variables or two elements
within a list but don't worry too much
about this particular method okay just a
quick reminder you can go to CH dojo dot
io / Python for to download the sample
file and the best way to support me
would be through my patreon page and you
can find that at CH dojo dot IO / PT ok
I'm working from CH dojo and I'll see
you guys in the next video