Quickly with Python - 08 - Classes & Objects Video Lecture | Python- Mastering Development in Python - Software Development

good morning fellow programmers thank
you for joining me
I'm t-pain and welcome to another let's
learn feel free to ease this skip ahead
feature on the right hand side to jump
ahead to any specific sections or
examples today we'll be using Python 2.7
point 4 you can download it from Python
org slash get it today we'll be focusing
on classes this will build heavily on
past lessons so feel free to go back and
watch them again if anything if I'm
clear
alright so classes what are they so
classes are way of packaging variables
and functions together for instance say
we wanted to create a character and a
video game this character would have
attributes and actions that he can do
for instance he'd have health he have a
weapon to start out with etc and these
would be his attributes or variables
that we store specific stuff in and the
things that he can do are specific
functions like he can attack he can run
he can explode who cares so how do we
use them well let's go ahead and create
on our desktop a class file and I'm just
going to do that doing by creating a
text document we're going to call this
class's underscore example dot py ok
it's asking me if I want to change the
file extension click yes all right and
then I'm going to go ahead and right
click and edit with idle all right so I
have idle open um I have the Python file
down below and then the shell up above
all right so let's go ahead and begin
with typing a very short classic example
the way you start out declaring a class
is using keyword class it's all
lowercase so CA ll I can't spell CLA SS
space and then typically with classes
you'll always always want to start out
the first letter uppercase the rest of
it
lowercase unless there's multiple words
then you make those uppercase start out
uppercase as well so we're going to type
test capital T lowercase e s T : enter
and just type Pass PA SS as you may
remember from before that's just
placeholder' doesn't do anything just
says hey just skip past this Python
alright and after that we're going to
type X equal space and then test open
closed parentheses just like we would
for calling a function and then press
Enter and we're done save it and then
press f5 on the keyboard or you can go
up to the run on the menu bar and then
run module right there alright and it
worked
alright so there was no errors returned
and it just created that class then the
program ended cool that's exactly what
we wanted excellent work all right so
within classes you'll notice that you'll
be using this key word self and it'll be
referring to anything that is its own
function or its own variables so if
you're ever having any issues with
creating classes double check that
you're using the key word self within
the arguments of the functions self is a
way of saying hey this function is
attached to me or this is my function
the same goes for variables which we're
going to be creating in just a bit so
for now we're going to ahead and clear
out this file and we're going to start a
new class this one's going to be a class
uppercase P lowercase H : enter and then
we're going to begin declaring our
function so we start with d EF space
lowercase print uppercase ham and then
begin the arguments and here the very
first argument we're going to put in
itself we're not going to put in any
other arguments but if you were to you
would use a comma and then put in
wherever you wanted right there okay so
we're going to go ahead in the
parentheses colon enter print and then
in quotations ham enter and we're done
creating our class so now we're going to
go ahead and create an instance of the
class in order going to do that with x
equals uppercase P lowercase H open
close parenthesis enter and then we're
just going to call that function using
the dot accessor so X dot print ham open
close parenthesis enter save and then
we're going to run it pressing f5
perfect so we didn't have any errors or
turned and it actually printed out him
our function worked exactly as we had so
our class example worked great but what
happens if we don't include self well
let's go ahead and try that out
I'm going to delete self save press f5
again to run and we're going to get a
type error and notice what the air at
says print ham takes no arguments but
one was given that one that was given
was actually the self that wasn't here
so we can really quickly fix that by
tabbing self back in so if you ever run
into this error you'll know that you're
missing self and they're probably
alright so next we're going to declare a
constructor or a initialization function
for this class alright so what is a
constructor a constructor is a function
that is called when the class is created
it is in charge of all the setup work
for a class for example if we wanted our
character to have some default health
and weapons when he started the game
this is where we would put them all
right so we're going to change our
current class to include a canoe
constructor we're going to go up to the
very top and press ENTER to add in
another definition so def underscore
underscore and Nitz underscore
underscore open parenthesis self close
parenthesis colon enter and next we're
going to type in self dot y as equal to
five save and then at the very end of
the file we're going to go ahead and try
to access that variable Y so what is
this function that we just created this
is the constructor double underscore in
it double underscore is the name of the
function that Python uses to construct
stuff when it's initially created you're
always going to want to include self in
the arguments and then any variables or
any functions that you wish to access
within itself you're going to use self
dot whatever the variable name or the
function name is this is saying hey this
is my variable if I were to create
another variable like Z for example I'll
show you what will happen at the very
bottom of the file go ahead and type
print space X dot Y and this will print
out the Y parameter that we plugged in
then after that type print X dot z save
and go ahead and run this we should
expect to find an error
right let's look at what happens up
above we had to hand print out because
we ran that function print ham worked
great then we printed five which was the
variable that was attached to the class
object and then and then we try to
access variable Z however we did not
include self dot in front of the Z so
this variable was created locally within
the function and the newest deleted
after it executed so this variable Z was
not stored within the class and so it
returned this attribute error saying
that there was no instance of Z within
it perfect so that's exactly what we'd
expect to happen all right so what if we
wanted to access functions within other
functions well it's very simple just the
same way that we can access variables
within the class we can access functions
so right here I'm going to actually call
this print hand function right here
within it in the init so we should see
it as soon as it's constructive it will
call this function so I'm going to type
in self dot print ham open close
parenthesis we do not need to include
self within this within the arguments
it's only within the definition of the
function itself and now I'm going to
delete those final two lines so that
we're only creating the class instance
we're not actually calling the function
outside of itself all right so go ahead
and click Save and then press f5 on the
keyboard to run it perfect so you saw
ham printed out because this function
was called within the initialization or
the constructor of the pH class perfect
great job all right
so next we're going to actually create
our own hero class and we're going to go
ahead and clear out this file that we
currently have all right so let's begin
by typing class capital H for the hero :
enter def underscore and Nitz underscore
self and then we're going to plug in
another argument called name then the
parameters and then end it with a colon
enter and now what we're doing is we're
saying hey we're going to pass in a name
now we need to store it within the
character so we're going to do that by
typing self dot name
is equal to
enter and so any name that we pass into
the arguments will be stored right
attached to the class perfect after that
we're going to type in self dot health
is equal to 100 enter and we're going to
create another function within this
class so we're going to go an unintended
open parenthesis and we're going to type
self because that has to be at the
beginning of every function that within
this class and we're going to type in
food close parentheses colon enter and
then we're going to include a simple
if-elsif statement to check for what
food is being passed in to the arguments
so we're going to type in if open
parentheses food is equal to and that's
double equal to check for something and
I'm going to check if it's equal to
Apple in quotes in parentheses : enter
self dot health is - equal to 100 why
why are we taking my health this guy's
allergic to apples
unfortunately so he's going to die as
soon as he eats an apple all right so
we're going to an indent and then type
Elif open parenthesis food is equal to
ham close parenthesis : enter self dot
health is plus equals 220 perfect and
we're done creating this class we're
going to unint all the way back down and
now we're going to wrap up the file by
creating this in actual class instance
of this so Bob is equal to hero and then
open parentheses and they're going to
punch in his name which is Bob of course
click in the quotations in parentheses
enter so we're going to go ahead and
double check everything now by typing
print Bob dot name print bob dot health
and then bob dot eat and then we're
going to feed him an apple to see what
happens
and that Apple is just a string enter
and then finally we're going to print
Bob's health again Bob health and now
we're done all right so to review we've
declared a class definition we've
declared an instance right here if Bob
is equal to the hero we've printed the
name
we printed the health he eats an apple
and then we print his health again
alright let's go ahead save f5 to run it
Oh
so I ran into the error because I
misspelled health up top so I'm gonna go
ahead and fix that real quick health
save and press f5 to run again
perfect all right so what's returned to
us Bob the name is returned first
excellent that's what we had expect and
then Bob's health is returned at a
hundred he eats the Apple which he's
allergic to and then he has zero health
perfect let's go ahead and punch in ham
in here to make sure that our ham is
working ham save f5 run perfect we get
120 health excellent all right so we're
going to wrap up this example by adding
some documentation for the hero now in
other examples we've had a documentation
be added to within the function right
here by using triple quotations and then
ending it and we can punch in like
whatever we want right here right you
can also do that the same way for
classes so we're going to have triple
quote enter enter triple quotes and then
punch in whatever we want worth in here
so we're going to ahead and punch in a
quick string saying a hero who is
allergic to apples so this documentation
is key because for any coders or anybody
else creating instances of this down the
road they have this clarify what this
class actually does all right so this is
the end of the Python basics series
congratulations on making it so far
excellent work you now know the basics
and fundamental stuff that makes Python
Python I will be starting up an
intermediate series soon so keep an eye
out for that please subscribe so you
don't miss it when it comes out we'll be
covering intermediate topics like
object-oriented programming inheritance
UML Python QT Python with Maya reading
and writing files thank you so much for
watching great job keeping up definitely
take a few minutes to investigate this
final example please leave a comment
below if this helped you at all and
please do me a huge favor and subscribe
to my channel thank you for all your
support and keep the dream alive