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Let's Make a Class!
4:21With vocabulary out of the way, let's see how to define our own classes.
Now we can base our class on
Python's built in classes.
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But that's a complicated
thing to start on.
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So instead let's start by creating
brand new classes from our imagination.
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Let's create a class that would represent
a character in a role-playing game.
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I like to play a sneaky thief or
assassin characters.
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So I'm gonna make one of those.
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If you wanna make a wizard or
a warrior, go right ahead.
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So I'm here in characters.py.
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And I'm gonna type in class Thief.
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And just like that I have
a class of my very own.
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Well, okay, it won't compile but
it's a class.
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All classes in Python start
with the keyword class.
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This is just like when
you start a function.
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You have to use the def keyword.
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Then again like a function
next comes the class's name.
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By convention classes always have
to start with a capital letter.
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If they have multiple words in them,
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like let's say we were
doing class MeleeWeapon,
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then each word is capitalized.
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Now I don't need that class so
I'm gonna go ahead and delete it.
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So to be a valid class,
it has to have something in it.
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The code block, right?
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Got the colon and everything.
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So let me put pass in here.
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And then I can test it out on the console.
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So I'm gonna go ahead and save and
then I'll come down to my console.
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And now if I go into Python,
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I can import my class and I can use it.
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So I'll say from characters import Thief.
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And then I will say that
kenneth is a Thief.
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So did I just called
a class like a function?
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Well you bet I did.
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But this didn't run the class.
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Not like it runs a function.
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Classes don't run.
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What this did though,
is it created an instance of the class.
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So now if I look at my variable,
I'll see some information about it.
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So check that out, yeah.
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It's an object.
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Specifically, it's an object
from character.Thief,
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which is the class name, right?
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So we have object, some characters.Thief.
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So cool.
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That's handy information.
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And this thing out here, the 0x7f blah,
blah, yours will be different.
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That tells me what spot in
memory my instance takes out.
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Okay, so what about attributes?
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How can I give my class some information?
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Well, I can define attributes
right inside the class,
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just like I would define variables.
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So, I'm a thief,
I'm probably sneaky, alright?
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Let's add that, so
we'll say sneaky = True.
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And we'll save that.
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And now I'm gonna go back
down here to my console.
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You may find yourself going back and
forth a whole lot.
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Simply because it's easier
to see what's going on.
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As you make incremental little changes.
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So from characters import Thief.
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And, kenneth = Thief().
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And then if I say.
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And I want to see what
the sneaky attribute has in it.
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I have to access that attribute.
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Python uses dot syntax to access
members of a class or an instance.
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And a member is anything
that's defined on the class.
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So attributes, methods,
that whole kind of thing.
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Right?
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Well I know the class
defined a sneaky attribute.
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So I should be able to get
to that with a dot right?
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kenneth.sneaky and I get back true.
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So cool.
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Now I can also get that on the class.
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If I do Thief.sneaky.
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I get that's true as well.
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Remember though that
instances are responsible for
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their own attribute values.
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So I should be able to change the sneaky
attribute just on my instance.
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So I'll do kenneth.sneaky = False.
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And now if I look at
kenneth.sneaky I get back False,
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not a very good thief then, I guess.
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But did that change the class?
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No, the class is still sneaky.
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Now, that's not always
true the other way around.
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I'd like you to play with that and
see what you can find out there.
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But I change my own sneakiness.
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And that won't affect any other
thief instances that I create.
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Like I said, there is a bit of
a gotcha without read and classes.
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You're not quite ready for it though.
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We'll come back to that in a little while.
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So long as you stick the changing
attribute values on instances you'll
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be fine.
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We can of course delete
instances of our class.
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Using the del key word.
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And now if I try to look at kenneth.
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I get a name error.
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Cuz it is not defined.
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All right.
I think you are ready for
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a code challenge about attributes.
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Get that done.
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And then come back.
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And we'll give your classes
some actions with methods.
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