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Re: Classes

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On Fri, 31 Oct 2014 13:18:00 -0400
Seymore4Head <Seymore4Head@Hotmail.invalid> wrote:

> On Sat, 01 Nov 2014 04:06:44 +1100, Steven D'Aprano
> <steve+comp.lang.python@pearwood.info> wrote:
> 
> >Seymore4Head wrote:
> >
> >> Because the topic of that lesson was getter setter.
> >> I can construct an __init___  but I was practicing get/set.
> >
> >What lesson is that? Using getters/setters is discouraged in Python.
> >
> >> This stuff is coming to me slowly.  I need to rinse and repeat quite a
> >> few more times, before I follow what is going on.
> >
> >Start with the simplest class possible:
> >
> >class MyClass:
> >    pass
> >
> >Right now, that class has a name, "MyClass", no methods, and no data. But we
> >can still create an instance. Call the class, as if it were a function, to
> >create the instance:
> >
> >obj = MyClass()
> >
> >What's the relationship between instances and classes? Classes are a general
> >type of entity, instances are a specific example of that entity. You can
> >have many instances from a class. So:
> >
> >Class: Dog
> >Instances: Rin-Tin-Tin, Lassie, Hooch (from the "Turner and Hooch" movie),
> >           Marmaduke, Gaspode the Wonder Dog, Spike the Bulldog, etc.
> >
> >Class: Wizard
> >Instances: Gandalf, Dumbledore, the Wizard of Oz, Rincewind, etc.
> >
> >Class: int
> >Instances: 0, 1, 2, -5, 23, 19874023, etc.
> >
> >
> >You can confirm that obj is now an instance of MyClass:
> >
> >print(isinstance(obj, MyClass))
> >
> >will print True.
> >
> >What can you do with obj? It has no interesting methods, and no data. But we
> >can give it some! Python, unlike some languages, allows you to dynamically
> >add data attributes to instances on the fly, without pre-defining them.
> >
> >obj.value = 23.0
> >obj.message = "hello world!"
> >print(obj.value)
> >print(obj.message)
> >
> >
> >will associate the data 23.0 and "hello world" to the attributes "value"
> >and "message" of the instance obj.
> >
> >Let's make the class a bit easier to use, at the expense of doing a bit more
> >work up front:
> >
> >class MyClass:
> >    def __init__(self, value, message):
> >        self.value = value
> >        self.message = message
> >
> >obj = MyClass(23.0, "hello world")
> >print(obj.value)
> >print(obj.message)
> >
> >
> >The __init__ method is automatically called when you call the class as if it
> >were a function. Because the __init__ method has two arguments (plus the
> >special "self" argument), you have to call the class with two arguments.
> >They get used as the value and message respectively.
> >
> >
> >Or we can give it getters and setters:
> >
> >class MyClass:
> >    def set_value(self, value):
> >        self.value = value
> >    def get_value(self):
> >        return self.value
> >    def set_message(self, message):
> >        self.message = message
> >    def get_message(self):
> >        return self.message
> >
> >obj = MyClass()
> >obj.set_value(23.0)
> >obj.set_message("hello world")
> >print(obj.get_value())
> >print(obj.get_message())
> >
> >
> >If you're thinking that's a lot of extra work for not much benefit, 99.99%
> >of the time you're right.
> 
> I agree it is more work.  But more work means more practice.  I need
> more practice figuring out how these commands work.
> 
> >obj = MyClass()
> >obj.set_value(23.0)
> >obj.set_message("hello world")
> >print(obj.get_value())
> >print(obj.get_message())
> 
> I don't know here to get more (simple) practice problems.  I am trying
> to invent my own.

Fine.  Practice problem that is actually Pythonic.  Define a Rectangle
class.  Give it length and width attributes, no unnecessary
getters or setters.  Give it perimeter() and area() methods.

Define a Square class, subclassed from Rectangle.  Use getters/setters
to enforce that the length and width must be equal.  Confirm that
length and width remain locked, and that perimeter() and area() work
correctly.

-- 
Rob Gaddi, Highland Technology -- www.highlandtechnology.com
Email address domain is currently out of order.  See above to fix.

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Classes   Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-30 16:16 -0400
  Re: Classes sohcahtoa82@gmail.com - 2014-10-30 13:33 -0700
    Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-30 17:00 -0400
  Re: Classes Rob Gaddi <rgaddi@technologyhighland.invalid> - 2014-10-30 13:34 -0700
    Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-30 17:00 -0400
  Re: Classes Larry Hudson <orgnut@yahoo.com> - 2014-10-30 14:28 -0700
    Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-30 17:34 -0400
      Re: Classes sohcahtoa82@gmail.com - 2014-10-30 18:21 -0700
      Re: Classes alister <alister.nospam.ware@ntlworld.com> - 2014-10-31 09:59 +0000
        Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 10:07 -0400
  Re: Classes   "ast" <nomail@invalid.com> - 2014-10-31 10:05 +0100
    Re: Classes   "ast" <nomail@invalid.com> - 2014-10-31 10:18 +0100
      Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-10-31 20:21 +1100
    Re: Classes   Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 10:05 -0400
      Re: Classes Ian Kelly <ian.g.kelly@gmail.com> - 2014-10-31 08:47 -0600
        Re: Classes Grant Edwards <invalid@invalid.invalid> - 2014-10-31 15:49 +0000
          Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 12:31 -0400
            Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-01 03:37 +1100
              Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 12:47 -0400
                Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-01 04:02 +1100
                Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 13:31 -0400
                Re: Classes Zachary Ware <zachary.ware+pylist@gmail.com> - 2014-10-31 12:39 -0500
                Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 13:57 -0400
                Re: Classes Rob Gaddi <rgaddi@technologyhighland.invalid> - 2014-10-31 10:40 -0700
                Re: Classes Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-11-01 11:17 +1300
                Re: Classes Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-01 12:06 +1100
                Re: Classes Ian Kelly <ian.g.kelly@gmail.com> - 2014-11-01 00:12 -0600
                Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-01 17:32 +1100
                Re: Classes Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-11-03 00:32 +1300
            Re: Classes Dave Angel <davea@davea.name> - 2014-10-31 13:20 -0400
            Re: Classes Marko Rauhamaa <marko@pacujo.net> - 2014-10-31 19:35 +0200
            Re: Classes Grant Edwards <invalid@invalid.invalid> - 2014-10-31 17:40 +0000
            Re: Classes Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-10-31 18:26 -0400
              Re: Classes Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-01 12:09 +1100
      Re: Classes   Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-01 04:06 +1100
        Re: Classes   Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 13:18 -0400
          Re: Classes Rob Gaddi <rgaddi@technologyhighland.invalid> - 2014-10-31 10:43 -0700
            Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 14:18 -0400
              Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 14:42 -0400
              Re: Classes Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-10-31 18:57 -0400
                Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 19:22 -0400
                Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 19:32 -0400
                Re: Classes Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-11-01 12:00 -0400
                Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-11-01 12:42 -0400
                Re: Classes Denis McMahon <denismfmcmahon@gmail.com> - 2014-11-02 09:50 +0000
                Re: Classes Tim Delaney <timothy.c.delaney@gmail.com> - 2014-11-02 21:32 +1100
                Re: Classes Denis McMahon <denismfmcmahon@gmail.com> - 2014-11-02 12:27 +0000
                Re: Classes Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-11-02 11:31 -0500
                Re: Classes Denis McMahon <denismfmcmahon@gmail.com> - 2014-11-03 03:12 +0000
                Re: Classes Dan Sommers <dan@tombstonezero.net> - 2014-11-03 06:29 +0000
                Re: Classes Denis McMahon <denismfmcmahon@gmail.com> - 2014-11-04 01:10 +0000
                Re: Classes Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-11-04 18:30 +1300
                Re: Classes Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-11-03 08:50 -0500
                Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-04 02:34 +1100
                Re: Classes Ian Kelly <ian.g.kelly@gmail.com> - 2014-11-03 07:47 -0700
                Re: Classes Larry Hudson <orgnut@yahoo.com> - 2014-11-02 14:03 -0800
            Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-01 07:51 +1100
              Re: Classes sohcahtoa82@gmail.com - 2014-10-31 14:24 -0700
                Re: Classes Rob Gaddi <rgaddi@technologyhighland.invalid> - 2014-10-31 14:40 -0700
                Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-01 08:56 +1100
                Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-01 08:36 +1100
          Re: Classes Grant Edwards <invalid@invalid.invalid> - 2014-10-31 17:43 +0000
    Re: Classes Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-10-31 14:11 +0000
    Re: Classes   Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 12:49 -0400
      Re: Classes   "ast" <nomail@invalid.com> - 2014-10-31 19:31 +0100
        Re: Classes   Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 14:36 -0400
        Re: Classes Joel Goldstick <joel.goldstick@gmail.com> - 2014-10-31 14:41 -0400
          Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 14:56 -0400

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