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so there's several different programming
paradigms and up until now in this

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course we've been mainly using the
imperative style of programming

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imperative programming involves
providing a series of instructions for

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the computer to follow in a defined
order now object oriented programming

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aims to combine data and the processes that
act on that data into objects which is

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called encapsulation

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before I continue it's important to
realize that the different paradigms are

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not necessarily exclusive and
object-oriented programming makes use of

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imperative programming within the
methods that objects used to manipulate

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the data also as we will see shortly our
imperative programming in Python has

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actually made extensive use of objects
we just didn't know that so the approach that

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we've been using so far in the course is
very similar to a recipe for cooking a

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meal so the recipe starts with the
ingredients and utensils it will be need

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which corresponds to a programs data
and then continues with the description of

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the steps that must be performed on that
data to produce in this case for the

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recipe

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finished meal an object oriented
approach relies on the objects such as

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the eggs milk spoon etc knowing
how to perform certain operations so

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the program just tells them to do so

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concept of an egg that knows how to fry
itself is a little bizarre but that

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really shows that the imperatives
approach to cooking a meal is more

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appropriate than an object-oriented
approach

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now a good example of the encapsulation of
data and function might be self lighting

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cigarettes well actually its a
bad example and I certainly wouldn't

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want to suggest that smoking is good but
it does demonstrate the concept quite well

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so without object oriented programming
the steps to smoking a cigarette might

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be place cigarette in mouth that's number
one number two light match number three

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hold match to cigarette and number four
inhale now encapsulating the functions

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that can be performed on the cigarette
into the cigarette reduces the code to

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place cigarette in mouth and inhale so
the cigarette knows how to light itself so

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that's not something that the smoker
needs to be concerned with

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the details of how it lights itself are
built into it when it's manufactured or

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in the case of programming it's
programmed into it when it's defined

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and the actual implementation is of
no interest to anything that uses the

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object now I've exercise a little license
they're self lighting cigarettes were

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produced for short time the 1960's
coincidentally around the same time that

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object oriented programming was
conceived and had a igniter

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built into them that had to be struck like a match
the advanced type that I described only

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existed in science fiction stories now
modern electronic cigarettes take this

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concept a little bit further but it's
only the details of the implementation

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that have changed so the method use
remains pretty much the same as the

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science-fiction variety now that's important
concept of object oriented

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programming as we will see replacing one
object with another one that performs

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the same task without having to concern
ourselves with the details of how it

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performs the task is central to object
oriented programming so another and

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hopefully much more healthier example
might be an electric kettle now the

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imperative approach to boiling water
for hot drink might be step 1 fill kettle with

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water

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step 2 light stove step 3 place kettle on stove step 4 for monitor kettle until

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water boils step 5 make the drink now it would then have to be a function that

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deals with lighting the stove which might
involve further functions to collect

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water or coal or was switched on the gas a
function to light the match and so on but

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in object orientated terms a kettle would have a
boil method that is triggered by

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operating a switch so the object
oriented program comes down to step

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one fill kettle with water

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step 2 switch kettle on step 3 when kettle switches off make drink so the

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imperative approach will also have to
identify the type of stove being used as

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its futile and probably a bit dangerous to hold a match to electric cooker

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now these examples may make it look like
we've got something for nothing because

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performing the tasks using an object
oriented approach involves fewer steps

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but there's no magic involved here now the
steps are still had to be programmed

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but their built into the objects
so that anything that using the object doesn't have to be

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concerned about them so the object orientated kettle has been built to contain an

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element or whatever method it employs could
be a ceramic disc or even a small

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nuclear reactor and the operation of
the heating mechanism has been wired up to

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the switch where the kettle was made so a lot
of work has gone into the production on

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the kettle in other words far more so that
the work that goes into making a kettle

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for use on the stove but subsequent use
of the kettle is there much easier

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because it knows how to perform its
function itself so one thing that may

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not be obvious and I haven't yet mentioned is that
everything in Python is an object so Python

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is unusual in this respect because even though Python uses objects extensively you

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don't actually have to be aware of that
to use so Python can be used for

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object-oriented programming but can also
be used to write purely imperative

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programming code so in fact the
Wikipedia entry for Python which I'm going to just load

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up the screen now you can see the link
in the top left hand corner you can see

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just down here it says that Python
supports multiple programming paradigms

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including object oriented imperative and
functional programming or procedural

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styles so in Java which is considered a
class-based object-oriented language

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there are primitive types such as an

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int and a double so if you've come to Python
from Java the following code which I'm

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about to show might seem very odd at
first so lets just go back to IntelliJ and I've created a

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new project here and a new Python file so if
you come back come from Java type in

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code like this....

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....so if we just run this see that it does

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work and we get the same result each time so line 3...and

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that's pretty normal for a programming
language like Java

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but the code on line 4 would probably be a bit bizarre and that's because the a even though

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it's been defined as you can see on line
12 as a number you could see that a has

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got an add method even though its an integer so if I command click add

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and that is control click on a PC or Linux you can
see that there's a method this is the

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built-ins definition of the add method and
interestingly enough if I go back to oop

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our file and click on the plus note that it has gone to the same method in the built ins

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so what you can see by that is that whether
you use this __add__

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or use a plus it's calling
the same code that is built-in

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builtins.py file and in this case add
two numbers together and smart enough to

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figure out the parameters you can see
there that the second argument in the

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case of line 3 is then added and line 4
the parameters b is added to the value

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of a now if this is your first
programming language and either you see

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nothing at all strange about this
or it will make very little sense but don't worry

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I'm gonna explain what it all means but
I wanted to warn you that you know if

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you've come from other programming
languages such as Java or C++ you

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probably gonna see some aspects of Python that seem surprising to you at

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least initially now when I said that
everything in Python is an object I meant

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everything even types are
implemented as classes now I will come

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back to that but for now I'm gonna focus
on making sense of what I've just done

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their so object-oriented programming uses
classes and methods to provide object

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that encapsulates both data and the
functions that operate on that Data now the

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method is just another word for function
and you have seen me use those terms

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interchangeably in this course but being big
correct here when a function is part of

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a class in Python we call it a method
now in Python there is a slight

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difference between a function and a method but writing a method is the same

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as writing functions now what we gonna
do is start with a very simple example

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to introduce the concept of a class and
show how classes work in Python now this

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example be a simple implementation of
the electric

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kettle so let's go ahead and do that's
so close the run window and I'm just gonna

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delete this code and we start by creating
a kettle class and its gonna model an

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electric kettle

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so.....and notice how its has been indented for us

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automatically and we're going to create a
method so....

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....

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....will talk about this shortly...

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we just type in the code for now so...

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....

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...so looking at this it can be helpful to
think of a class as a template from

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which objects can be created so when we
create objects of this kettle class they

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all have a name and a price now they won't
have the same name nor the same price

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each instance of the class will have its
own values for name and price so classes

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as I said is a template from which objects
can be created and all the objects

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created from the same class will share
the same characteristics now an instance

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is just another name for an object created from a
class definition so if I now create a

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kettle called Kenwood then Kenwood will be an
instance of the kettle class you can also

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say that kenwood is an object of
type kettle so I'm gonna create a couple of

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kettle objects so we can see this in
practice so let's continue typing and

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we will go to line 8 here and type...

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....

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.....

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.....and lets make another kettle...

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...and I should really have two lines there

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separating the class definition to be
consistent with our code so the code on

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line 9 creates an instance of the kettle
class and we've given it the name

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kenwood and other instances is created on line 16 and this time it's called the

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Hamilton so each instance has its own
values for naming and price and their access

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by using . annotations so we type in Kenwood.price or Hamilton.make for

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argument sake to access that information
so a good analogy here is for plans for

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building a house so the plan itself just
describes what the house will look like

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its size how many rooms it will have etc
now this is similar

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the plan to the class which is just a
template for creating objects once you

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have a plan you can then create it as many
houses as you want based on that

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plan and the same is true of classes
once a class has been defined like how

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kettle class that we define on line one
we can then create as many instances of that

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classes as we want now just as you can't do
anything with the house plan other than

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build houses based on it you can't
really do anything with the class other

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than create instances of it once the
instances have been created you can then call

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their methods and access their variables so
on line 11 Kenwood.price retrieves

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the price from the instance called
Kenwood and Hamilton.price will get the

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price of the Hamilton instance we can
also give the price a new value as we see on line

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13 where we set the price to $12.75 so we've been
using dot notation extensively in our

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programs in this course

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when you seen that when we've used the
append method to add items to a list for example

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also all the TK widgets are objects
that have .pack and grid methods amongst

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many others to allow them to be placed
in the window manager so lets add another

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example in this program so I'm going to start typing and put on some code on line 18

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gonna type...

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.....

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....and you can see here models kenwood equals$12.75 and Hamilton equals $14.55 so it's

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retrieved the values out of each
instance of the 2 kettle objects that

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we've created so the parameters in the format
method are the make price data attributes of

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the Kenwood and Hamilton objects
another bit of jargon here the

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attributes so we've become used to
talking about variables but when a

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variable is bound to an instance of a
class then it's referred to as a data

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attribute in Python now their other
object-oriented programming terms for

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the same things you might find variable
attributes also called fields in

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languages such as Java or data members
in C++ now I'll introduced yet another term

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shortly probably in the next video one
that's been borrowed from the small talk

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language but lets end this video here and in then next
video we'll continue our discussion about

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objects see you in the next video