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ok so in the last video we had a lot of

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talk about polymorphism lots of slides

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let's now see how this all relates to

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python code now we're going to use this

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code again in the next section so we're

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going to create a new python file so

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lets create one new python file and

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will call this one ducks

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ok and i know it's taking awhile a few

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videos ago I mentioned that there was a

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discussion on ducks so

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we're going to start out now with a duck

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class....going to

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define a few functions....

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...

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...

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....

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...

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....

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....so it's a very

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simple class I haven't even created init

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method so our ducks do have three methods

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walk swim and quack and by the way

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because we haven't created a init

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method we are getting a warning here the

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method walk maybe static will ignore

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that for now

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alright so what we want to do now is

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create a function to test our duck class

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so i'm going to come down here and we're

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going do...

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...

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so the test duck function takes a single

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argument and calls it's walk swim and

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quack methods so i'll create a new duck

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and see how it behaves now we may need

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to import our ducks into another module so

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make sure that the main code doesn't run

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if ducks is imported and if you recall we

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did see how to do that in a previous

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section so let's go ahead....

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....

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...

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...

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...so lets run this

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you can see down here when I ran it that

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donald walks like a duck swims like a

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duck and also quacks like a duck

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alright so now that we've done that

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let's add another class a penguin class

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i'm going to add it after the Donald

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class finishes leaving two black lines

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between it so will call this one

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class...

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...

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...

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....

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...

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...

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ok so you can say what we've done there and

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added some slang there for those you who not

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sure what I've done it are you having a

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laugh okay so we've created both the duck

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class now and a penguin class now it's clear

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that the penguin isn't a duck but it

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happens to have exactly the same methods

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as our duck class and consequently we

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can do exactly the same things with it

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and we can do something here like Percy....

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....

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....let's try running that

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so you can see here that our test_

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duck function still works now

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percy may will be behaving a little bit

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strangely by duck standards but as far

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as the test_duck functions

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concerned percy walks like a duck

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swims like a duck and quacks like a duck

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as far as the test_duck

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function is concerned

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Percy is a duck so in other words our

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Penguin's passing the duck test what

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I'm going to do is switch to the browser now

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and open up a link a wikipedia link

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paste in the link as always and

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close this huge message that's

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appearing on the screen there maybe

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later

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close ok as you can see it says so the

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duck test is a humorous term for a

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form of reasoning and boils down to

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being able to tell what something is by

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how it behaves and the phrase is

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attributed to an American poet James

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Whitcomb raleigh and his original phrase

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was when I see a bird that walks like a

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duck swims like a duck and quacks like a

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duck

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I'll call that bird a duck

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so what's the point of all this well that

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approach is fundamental to the way that

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python deals with objects unlike

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statically typed languages that require

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the type of every object to be declared

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when it's used pythons dynamic typing

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means that it's only really interested

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in what can be done with an object if an

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object has the necessary attributes then

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python quite happy for it to be used

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now the phrase is commonly used in

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dynamically type languages like python

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and you'll often hear them referred to

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as duck type in fact we saw it in one

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of the warnings and IntelliJ gave

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earlier in the course and that warning

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said due to dynamic dispatch and duck typing

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this is possible with a limited but

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useful number of cases now we know that

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penguins aren't ducks and Percy has an

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inherited any of these duck like behavior

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from a common subclass the important

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thing is that percy has the methods

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that our test_duck function relies

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on and so as far as python is concerned

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Percy is a duck so i'll stop the video

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here now and in the next video we're

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going to have a look at implementing

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polymorphism using something called

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composition see you in the next video