Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 7: Wizard Battle App
Lecture: Modeling with classes
0:00 So we have the basic structure of our game built
0:02 and now it's time to start working with the actors and the payers in the game,
0:06 the wizards and the creatures and defining them and their relationships,
0:11 and that's where this is going to get really interesting.
0:13 We are going to move this stuff around in the end,
0:15 but let's put it here for now,
0:16 we are going to have a set of creatures
0:18 let's just take this a list in the beginning
0:20 and we'll figure out what goes into this list it'll be empty for the moment
0:24 but we'll come up with some creatures to put in there
0:26 and we are also going to have a wizard and let's call it our hero,
0:28 and we somehow want the thing to represent the wizard,
0:31 this hero is going to have to have actions and it's to battle the creatures,
0:35 and it's going to have to have data like the remaining hit points
0:39 or the level or something like that,
0:40 so let me just write none for a second
0:42 so say this points add nothing until we get the chance to define
0:47 how we are going to represent the wizards.
0:49 So I could come over here and I could write the code,
0:52 just in this space, right here,
0:54 I can create a class that represents the behaviors
0:58 and the data associated with our hero wizard.
1:00 But I don't want to do that, let's try to organize this a little bit better,
1:04 when I have a lot of pieces involving the creatures and the wizards and so on
1:09 so let's come over here and make a new Python file
1:11 and we'll call it actors, we'll call it creatures or players or whatever.
1:15 One of the real powerful ways we can model both behavior and data in Python
1:20 and in many programming languages
1:22 is with this object oriented programming concept,
1:25 and we start by creating a blueprint
1:27 from which we will build out instances, of these classes,
1:32 we'll build out a particular type of wizard,
1:34 maybe we will have a hero wizard and an evil wizard or something to this effect.
1:39 So the blueprint is called a class, when we define it it's just class,
1:44 remember, we used def for methods,
1:46 for classes, we just say class and then we just give it a name,
1:50 notice, in Python most things have lower case names,
1:53 game loop, creatures variable, hero, keywords and so on,
1:57 but for classes, they are typically cap words style,
2:01 so like Wizard or earlier we worked with Beautiful Soup,
2:04 where the B and the S were capitalized, right,
2:06 so we are going to define a Wizard, and we'll name it like that
2:11 and we can just say pass to say we don't want to define
2:14 any data or any behaviors in the beginning.
2:17 Let's do the same thing for creatures,
2:18 we'll create a class called creature
2:21 and we'll just say pass for the moment
2:23 so let's go back here and we'll use those,
2:26 instead of saying none, that wasn't so amazing,
2:29 I'd like to say Wizard, well, that's not working so well,
2:33 PyCharm says I have no idea what this means wizard,
2:36 just like any function or variable defined it in another module
2:39 we have to import it, so let's go at the top and import our wizard.
2:43 Typically, I prefer the type of import that retains the name space
2:47 so it's very clear where something came from,
2:49 so I can say actors and then down here I could say this
2:52 I could go over here and say actors.
2:54 and then you could see my creature and wizard
2:56 and the way we create an instance of a class
2:59 is we call the initializer just like this.
3:03 Now wizards and creatures are so fundamental to the behavior of this game,
3:07 that I am going to use a different import,
3:09 I am going to come over here and say from actors import
3:14 and then we get a list, what do you want to import,
3:17 wizards and let's go and import the creature while we are at it,
3:19 so if we write it like this then we don't have to use the name space,
3:22 we can just come down here and say wizard,
3:25 in fact we are not even allowed to use the name space
3:27 and here let's put some creatures, so we'll create a new creature,
3:30 what we want to do is initialize this
3:32 with the various specific details of this creatures,
3:36 so remember we had a toad, he was pretty weak, we had a tiger,
3:39 we had a dragon, we had an evil wizard,
3:41 we haven't set that part yet so let's just put a bunch of creatures into our list here.
3:45 So now we have a list with five creatures here
3:48 and we have one particular hero,
3:51 now if you wonder why these are gray and have squiggles
3:53 that's just because we are not doing anything with them, yet.
3:55 Let's go and run this and make sure things are hanging together.
3:58 All right, if we get to this far, things must be going great.