Raising objects

[Steven Taschuk]

Quoth Jan Olderdissen:
  [...]
> That said, I question the point of deriving from object as classes
> (and in fact all objects as far as I can tell) are derived from object
> as it is. [...]

Depends what you mean by "derived".  On the one hand, both old-
and new-style instances are instances of object according to
isinstance():

    >>> class OldStyle: pass
    ... 
    >>> class NewStyle(object): pass
    ... 
    >>> o = OldStyle()
    >>> n = NewStyle()
    >>> isinstance(o, object)
    1
    >>> isinstance(n, object)
    1

But on the other hand, old-style classes are not subclasses of
object:

    >>> issubclass(OldStyle, object)
    0
    >>> issubclass(NewStyle, object)
    1

For example, they do not inherit attributes from object:

    >>> dir(object)
    ['__class__', '__delattr__', '__doc__', '__getattribute__', '__hash__', '__init__', '__new__', '__reduce__', '__repr__', '__setattr__', '__str__']
    >>> n.__reduce__
    <built-in method __reduce__ of NewStyle object at 0x815045c>
    >>> o.__reduce__
    Traceback (most recent call last):
      File "<stdin>", line 1, in ?
    AttributeError: OldStyle instance has no attribute '__reduce__'

> [...] Since object isn't a class, deriving from it probably is
> bogus to begin with. [...]

Not at all; it's exactly the right way to make a new-style class,
which is (among other things) needed to get properties to work:

Right:

    >>> class NewStyle(object):
    ...     x = property(lambda self: 3)
    ... 
    >>> n = NewStyle()
    >>> n.x
    3
    >>> n.x = 2
    Traceback (most recent call last):
      File "<stdin>", line 1, in ?
    AttributeError: can't set attribute

Wrong:

    >>> class OldStyle:
    ...     x = property(lambda self: 3)
    ... 
    >>> o = OldStyle()
    >>> o.x
    3
    >>> o.x = 2 # shouldn't be able to do this!
    >>> o.x
    2

What *is* bogus imho is the distinction between old- and new-style
classes.  (It exists for historical reasons; eventually old-style
classes will disappear, I presume and hope.)

-- 
Steven Taschuk             "The world will end if you get this wrong."
staschuk at telusplanet.net     -- "Typesetting Mathematics -- User's Guide",
                                 Brian Kernighan and Lorrinda Cherry