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With vocabulary out of the way, let's see how to define our own classes.
We'll be doing a lot of importing in this course because it gives us the best way of organizing our code into logical bunches. It's a good practice to get into!
Notice that we can immediately read and write our class attributes! We don't usually write getters or setters (methods for retrieving or updating data on an instance) in Python.
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Now we can base our class on
Python's built in classes.
0:00
But that's a complicated
thing to start on.
0:03
So instead let's start by creating
brand new classes from our imagination.
0:05
Let's create a class that would represent
a character in a role-playing game.
0:10
I like to play a sneaky thief or
assassin characters.
0:13
So I'm gonna make one of those.
0:16
If you wanna make a wizard or
a warrior, go right ahead.
0:18
So I'm here in characters.py.
0:20
And I'm gonna type in class Thief.
0:22
And just like that I have
a class of my very own.
0:25
Well, okay, it won't compile but
it's a class.
0:29
All classes in Python start
with the keyword class.
0:32
This is just like when
you start a function.
0:35
You have to use the def keyword.
0:37
Then again like a function
next comes the class's name.
0:39
By convention classes always have
to start with a capital letter.
0:43
If they have multiple words in them,
0:47
like let's say we were
doing class MeleeWeapon,
0:48
then each word is capitalized.
0:54
Now I don't need that class so
I'm gonna go ahead and delete it.
0:56
So to be a valid class,
it has to have something in it.
0:59
The code block, right?
1:02
Got the colon and everything.
1:03
So let me put pass in here.
1:05
And then I can test it out on the console.
1:07
So I'm gonna go ahead and save and
then I'll come down to my console.
1:09
And now if I go into Python,
1:13
I can import my class and I can use it.
1:16
So I'll say from characters import Thief.
1:19
And then I will say that
kenneth is a Thief.
1:23
So did I just called
a class like a function?
1:27
Well you bet I did.
1:30
But this didn't run the class.
1:31
Not like it runs a function.
1:33
Classes don't run.
1:34
What this did though,
is it created an instance of the class.
1:36
So now if I look at my variable,
I'll see some information about it.
1:40
So check that out, yeah.
1:43
It's an object.
1:45
Specifically, it's an object
from character.Thief,
1:46
which is the class name, right?
1:49
So we have object, some characters.Thief.
1:51
So cool.
1:54
That's handy information.
1:55
And this thing out here, the 0x7f blah,
blah, yours will be different.
1:56
That tells me what spot in
memory my instance takes out.
2:01
Okay, so what about attributes?
2:05
How can I give my class some information?
2:07
Well, I can define attributes
right inside the class,
2:11
just like I would define variables.
2:15
So, I'm a thief,
I'm probably sneaky, alright?
2:18
Let's add that, so
we'll say sneaky = True.
2:22
And we'll save that.
2:25
And now I'm gonna go back
down here to my console.
2:26
You may find yourself going back and
forth a whole lot.
2:29
Simply because it's easier
to see what's going on.
2:31
As you make incremental little changes.
2:34
So from characters import Thief.
2:36
And, kenneth = Thief().
2:38
And then if I say.
2:42
And I want to see what
the sneaky attribute has in it.
2:44
I have to access that attribute.
2:47
Python uses dot syntax to access
members of a class or an instance.
2:49
And a member is anything
that's defined on the class.
2:53
So attributes, methods,
that whole kind of thing.
2:56
Right?
2:59
Well I know the class
defined a sneaky attribute.
3:00
So I should be able to get
to that with a dot right?
3:03
kenneth.sneaky and I get back true.
3:05
So cool.
3:09
Now I can also get that on the class.
3:11
If I do Thief.sneaky.
3:14
I get that's true as well.
3:16
Remember though that
instances are responsible for
3:18
their own attribute values.
3:20
So I should be able to change the sneaky
attribute just on my instance.
3:22
So I'll do kenneth.sneaky = False.
3:27
And now if I look at
kenneth.sneaky I get back False,
3:30
not a very good thief then, I guess.
3:34
But did that change the class?
3:36
No, the class is still sneaky.
3:39
Now, that's not always
true the other way around.
3:41
I'd like you to play with that and
see what you can find out there.
3:44
But I change my own sneakiness.
3:47
And that won't affect any other
thief instances that I create.
3:49
Like I said, there is a bit of
a gotcha without read and classes.
3:53
You're not quite ready for it though.
3:57
We'll come back to that in a little while.
3:59
So long as you stick the changing
attribute values on instances you'll
4:01
be fine.
4:04
We can of course delete
instances of our class.
4:05
Using the del key word.
4:08
And now if I try to look at kenneth.
4:10
I get a name error.
4:11
Cuz it is not defined.
4:12
All right.
I think you are ready for
4:14
a code challenge about attributes.
4:15
Get that done.
4:16
And then come back.
4:17
And we'll give your classes
some actions with methods.
4:18
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