[Python-Dev] copy confusion

[Fredrik Lundh]

back in Python 2.1 (and before), an object could define how copy.copy should
work simply by definining a __copy__ method.  here's the relevant portion:

    ...
    try:
        copierfunction = _copy_dispatch[type(x)]
    except KeyError:
        try:
            copier = x.__copy__
        except AttributeError:
            raise error, \
                  "un(shallow)copyable object of type %s" % type(x)
        y = copier()
    ...

I recently discovered that this feature has disappeared in 2.3 and 2.4.  in-
stead of looking for an instance method, the code now looks at the object's
type:

    ...

    cls = type(x)

    copier = _copy_dispatch.get(cls)
    if copier:
        return copier(x)

    copier = getattr(cls, "__copy__", None)
    if copier:
        return copier(x)

    ...

(copy.deepcopy still seems to be able to use __deepcopy__ hooks, though)

is this a bug, or a feature of the revised copy/pickle design?   (the code in
copy_reg/copy/pickle might be among the more convoluted pieces of python
coding that I ever seen...  and what's that smiley doing in copy.py?)

and if it's a bug, does the fact that nobody reported this for 2.3 indicate that
I'm the only one using this feature?  is there a better way to control copying
that I should use instead?

</F>