[Edu-sig] Explaining Classes and Objects

[Kirby Urner]

> You might try: "These names don't just exist in some primordial soup.
> There has to be a place they get stored.  There is a bit of "magic":
>      import __main__
>      a = 24
>      print a, __main__.a
>      __main__.a = 365
>      print a, __main__.a
> 
> And even:
> 
>      print a, __main__.a, __main__.__main__.a
> 

After which I might go:

 >>> dir(__main__)
 ['__builtins__', '__doc__', '__main__', '__name__', 'a']
 >>> dir(__builtins__)

That'd  connect back to Laura's focus on exception handling -- clearly the
Error related content in __builtins__ is significant.

 >>> type(ArithmeticError)
 <type 'classobj'>
 >>> dir(ArithmeticError)
 ['__doc__', '__getitem__', '__init__', '__module__', '__str__']
 >>> ArithmeticError.__module__
 'exceptions'
 >>> EnvironmentError.__module__
 'exceptions'

 >>> import exceptions
 >>> dir(exceptions)

> Now everything is dot notation, with some of the "thing." stuff assumed.
> Eventually you'll have to say locacal variables don't really work like
> that, but they are close.
> 

universe.milkyway.sun.earth.hawaii.maui is another way to introduce
dot-notation.  It's about progressively zooming in, or out, through a
succession of progressively more, or less, encompassing domains.

This gets us back to the root class/object metaphor, which allows us to
appreciate the ordinary interaction of any two objects as involving
encapsulation, polymorphism and message-passing i.e. the original SmallTalk
paradigm.

Kirby

> 
> --Scott David Daniels
> Scott.Daniels at Acm.Org
>