confused about __new__

[Ian Kelly]

On Tue, Dec 27, 2011 at 3:19 PM, K Richard Pixley <rich at noir.com> wrote:
> Are you trying to demonstrate that I haven't prevented you from
> instantiating Foo?  If so, then I will cede that point.  I certainly don't
> know enough about python internals just now to even claim to be capable of
> protecting a class from a hostile user.  My guess is that short of a
> privileged/unprivileged split, or castrating the interpreter and locking you
> into it, such a protection would not be possible.

Yes, that was the point.  I certainly don't think that anybody should
ever be creating class instances by directly invoking object.__new__
unless they really, really know what they are doing.  I was just
pointing out that I don't think it's actually possible to prevent
classes from being instantiated.

> My point was that I can indeed intercept common and convenient usage to
> create a lovely singleton semantic.  I can't force you to use it. (Nor do I
> have any motivation to so do.)

Sure, I don't disagree with that.  And the object.__new__ workaround
is a general point that doesn't apply only to singletons.  Any class
that customizes its instantiation process can be messed up by doing
that.