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We can give our class some special abilities by defining methods for it.
You don't have to call the instance argument self if you don't want to. It's not a required name but it's a very common convention (I don't think I've ever seen code that didn't).
class Thief:
sneaky = True
def pickpocket(instance):
if instance.sneaky:
return bool(random.randint(0, 1))
return False
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If all we could do with classes is set and
0:00
use attributes, they wouldn't
be all that useful, would they?
0:02
Like I mentioned before, though,
0:04
we can give verbs to our
objects by creating methods.
0:05
Now, don't get too worried about methods,
cuz I'll let you in on a secret.
0:08
Methods are just functions
that belong to a class.
0:11
So, if you can write a function,
you can write a method.
0:13
They do have one little gotcha, though.
0:16
So, let's get into Workspaces so
I can teach you all about them.
0:17
So, I'm gonna simplify
things a little bit,
0:20
I'm gonna leave out a couple
of things here at first.
0:22
Methods in classes are the actions of
the instances of your class can do.
0:24
For example, my Thief class might have
a pickpocket method that lets it try and
0:29
snatch something out of
another person's pocket.
0:33
Methods belong to the class, so
they're indented inside of it,
0:36
just like attributes are.
0:39
So, we'll say def pickpocket and
that'll take an argument self and
0:40
then we'll return a bool of
random.randit between 0 and 1.
0:41
And that means I
0:41
need to import random.
0:46
So, what's this self thing
that's going on here?
0:57
What's that about?
1:01
Well, methods are functions
that's belong to a class.
1:02
Whenever they're used,
1:05
however, they're used by an instance,
not by the actual class.
1:06
Because of that, methods always
take at least one parameter,
1:11
which represents the instance
that's using the method.
1:14
Now, by convention that parameter's
always called self, but
1:17
you can call it anything you
want in your own classes.
1:21
But I highly recommend
you stick with self.
1:23
Now, the neat thing here is you
don't give any arguments to self
1:26
when you use the method.
1:29
Let's try this out down
here in our console.
1:31
So, Python from characters import Thief.
1:33
And kenneth = Thief just like before,
right?
1:37
So now, I can do kenneth.pickpocket().
1:43
And just like any other function,
I have to call it with parenthesis.
1:47
And since the method doesn't take any
arguments other than self I don't put
1:50
anything inside of here.
1:55
And I get back False, so
it randomly picked false.
1:57
So, cool.
2:01
Now, I don't usually like to show you
clunky ways of achieving something but
2:02
I feel like this whole self thing
needs a little bit more explanation.
2:06
Now, let's do the same method but
2:10
we're going to do it in a slightly
different way, all right?
2:12
So, if I tried to Thief.pickpocket().
2:15
Then I get an error.
2:19
I get this TypeError saying that
pickpocket is missing a required
2:20
positional argument, self.
2:23
Okay, so let's give it a self,
pickpocket, and
2:26
I'm going to give it
an instance of the class.
2:29
And this time I get False again.
2:33
So, we just ran the exact same code, but
2:35
this time we had to provide an argument
to pickpocket or it failed, right?
2:37
Since we called it
directly from the class,
2:41
we had to provide an instance
that it would be used by.
2:42
So, let's add a little something to
the class to make this instance use
2:46
more obvious.
2:49
I' m gonna go ahead and exit and
them I'm gonna clear this screen.
2:50
I'm gonna hop back up here to this.
2:54
Okay, so inside pickpocket
let's add a new line here,
2:55
print Called by, and
then let's fill that in with self.
3:00
So, now our instance will print out who
it is that's trying to pickpocket someone
3:05
else, okay?
3:10
Maybe not the best approach for
a thief but
3:11
we're here to learn not to
steal things from people.
3:13
So, from characters import Thief,
kenneth = Thief.
3:17
And now, let's do kenneth.pickpocket.
3:23
Okay, called by characters.Thief
object at that address, and True.
3:27
Cool, that time I succeeded, all right?
3:31
So now, let's try our other method of it,
Thief.pickpocket().
3:34
And we'll pass in the instance,
which is kenneth.
3:38
And I get the same output,
the exact same output, right?
3:42
Called by characters.Thief object
at 0x7f99b71edef0, all right?
3:45
Exactly same memory address.
3:50
So, the fact that we have the exact
same memory address shows us that it's
3:54
using the exact same object for
calling the method both times.
3:58
This self concept often trips
up early programmers, but
4:03
practice makes perfect on it.
4:07
And thankfully, Python will gripe at
you loudly if you forget to use self as
4:08
a parameter if you forget
to call it on a method.
4:12
All right, one more thing about self.
4:17
We can always use self to talk about
the current instance, like in the method.
4:19
So, let's check and
4:25
make sure that our thief is sneaky before
we even attempt to pickpocket somebody.
4:27
So, let's take out this print line.
4:32
Cuz we don't need that.
4:35
And let's say if self.sneaky,
and then we'll indent that.
4:36
Otherwise, we'll return False, okay?
4:41
So, if the instance's sneaky
attribute is set to True,
4:44
then we'll try and pickpocket.
4:49
Otherwise, we just always return a False.
4:51
All right, so that's cool.
4:53
Now let's give that a try.
4:55
Come back down here.
4:57
From characters import Thief.
5:01
kenneth = Thief().
5:03
And let's try this.
5:07
So, kenneth.pickpocket().
5:08
And we get false, and
if I run this another time or two I get,
5:10
yeah there we go, True, False, whatever.
5:13
Okay, so now let's make sure
that I am not sneaky, all right?
5:16
I'm a clumsy non sneaky thief.
5:21
And now, let's try kenneth.pickpocket().
5:24
False, False, False,
False, False, all right?
5:28
So, it's always False.
5:30
I'm gonna get caught cuz I'm not sneaky.
5:32
So, inside of a class's method,
self always refers to the instance.
5:36
And I can use that to get to
the instance's attributes and
5:40
even other methods.
5:43
Let's try this whole method thing
out with a co-challenge or two.
5:45
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