- What Are Objects And Classes? 2:45
- OOP Vocabulary Quiz 1 5 questions
- Let's Make a Class! 4:21
- Your first class 2 objectives
- Methods 5:48
- Your first method 1 objective
- Method Arguments 5:33
- Method Interactivity 1 objective
- __init__ 2 objectives
- Design 3:40
- OOP Basics 5 questions
- Master Class 3 objectives
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Methods
5:48We can give our class some special abilities by defining methods for it.
If all we could do with classes is set and
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use attributes, they wouldn't
be all that useful, would they?
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Like I mentioned before, though,
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we can give verbs to our
objects by creating methods.
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Now, don't get too worried about methods,
cuz I'll let you in on a secret.
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Methods are just functions
that belong to a class.
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So, if you can write a function,
you can write a method.
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They do have one little gotcha, though.
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So, let's get into Workspaces so
I can teach you all about them.
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So, I'm gonna simplify
things a little bit,
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I'm gonna leave out a couple
of things here at first.
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Methods in classes are the actions of
the instances of your class can do.
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For example, my Thief class might have
a pickpocket method that lets it try and
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snatch something out of
another person's pocket.
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Methods belong to the class, so
they're indented inside of it,
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just like attributes are.
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So, we'll say def pickpocket and
that'll take an argument self and
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then we'll return a bool of
random.randit between 0 and 1.
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And that means I
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need to import random.
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So, what's this self thing
that's going on here?
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What's that about?
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Well, methods are functions
that's belong to a class.
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Whenever they're used,
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however, they're used by an instance,
not by the actual class.
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Because of that, methods always
take at least one parameter,
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which represents the instance
that's using the method.
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Now, by convention that parameter's
always called self, but
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you can call it anything you
want in your own classes.
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But I highly recommend
you stick with self.
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Now, the neat thing here is you
don't give any arguments to self
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when you use the method.
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Let's try this out down
here in our console.
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So, Python from characters import Thief.
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And kenneth = Thief just like before,
right?
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So now, I can do kenneth.pickpocket().
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And just like any other function,
I have to call it with parenthesis.
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And since the method doesn't take any
arguments other than self I don't put
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anything inside of here.
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And I get back False, so
it randomly picked false.
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So, cool.
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Now, I don't usually like to show you
clunky ways of achieving something but
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I feel like this whole self thing
needs a little bit more explanation.
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Now, let's do the same method but
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we're going to do it in a slightly
different way, all right?
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So, if I tried to Thief.pickpocket().
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Then I get an error.
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I get this TypeError saying that
pickpocket is missing a required
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positional argument, self.
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Okay, so let's give it a self,
pickpocket, and
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I'm going to give it
an instance of the class.
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And this time I get False again.
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So, we just ran the exact same code, but
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this time we had to provide an argument
to pickpocket or it failed, right?
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Since we called it
directly from the class,
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we had to provide an instance
that it would be used by.
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So, let's add a little something to
the class to make this instance use
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more obvious.
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I' m gonna go ahead and exit and
them I'm gonna clear this screen.
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I'm gonna hop back up here to this.
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Okay, so inside pickpocket
let's add a new line here,
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print Called by, and
then let's fill that in with self.
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So, now our instance will print out who
it is that's trying to pickpocket someone
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else, okay?
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Maybe not the best approach for
a thief but
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we're here to learn not to
steal things from people.
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So, from characters import Thief,
kenneth = Thief.
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And now, let's do kenneth.pickpocket.
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Okay, called by characters.Thief
object at that address, and True.
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Cool, that time I succeeded, all right?
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So now, let's try our other method of it,
Thief.pickpocket().
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And we'll pass in the instance,
which is kenneth.
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And I get the same output,
the exact same output, right?
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Called by characters.Thief object
at 0x7f99b71edef0, all right?
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Exactly same memory address.
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So, the fact that we have the exact
same memory address shows us that it's
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using the exact same object for
calling the method both times.
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This self concept often trips
up early programmers, but
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practice makes perfect on it.
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And thankfully, Python will gripe at
you loudly if you forget to use self as
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a parameter if you forget
to call it on a method.
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All right, one more thing about self.
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We can always use self to talk about
the current instance, like in the method.
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So, let's check and
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make sure that our thief is sneaky before
we even attempt to pickpocket somebody.
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So, let's take out this print line.
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Cuz we don't need that.
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And let's say if self.sneaky,
and then we'll indent that.
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Otherwise, we'll return False, okay?
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So, if the instance's sneaky
attribute is set to True,
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then we'll try and pickpocket.
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Otherwise, we just always return a False.
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All right, so that's cool.
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Now let's give that a try.
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Come back down here.
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From characters import Thief.
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kenneth = Thief().
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And let's try this.
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So, kenneth.pickpocket().
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And we get false, and
if I run this another time or two I get,
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yeah there we go, True, False, whatever.
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Okay, so now let's make sure
that I am not sneaky, all right?
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I'm a clumsy non sneaky thief.
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And now, let's try kenneth.pickpocket().
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False, False, False,
False, False, all right?
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So, it's always False.
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I'm gonna get caught cuz I'm not sneaky.
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So, inside of a class's method,
self always refers to the instance.
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And I can use that to get to
the instance's attributes and
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even other methods.
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Let's try this whole method thing
out with a co-challenge or two.
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