[Python-Dev] PySet API

Barry Warsaw barry at python.org
Tue Mar 28 22:12:47 CEST 2006

On Tue, 2006-03-28 at 17:28 +1200, Greg Ewing wrote:
> Barry Warsaw wrote:
> > My PySet_Clear() raises a SystemError
> > and returns -1 when the object is a frozen set.
> Isn't SystemError a bit drastic? TypeError would be
> sufficient here, surely.

Possibly, but all the other PySet_*() functions call
PyErr_BadInternalCall() when they get a type they don't accept, so
PySet_Clear() should be consistent.

> > If PyObject_Clear() is implemented something like
> > 
> > int PyObject_Clear(PyObject *o)
> > {
> >     return (o->ob_type->tp_clear ? o->ob_type->tp_clear(o) : -1);
> > }
> > 
> > then you /would/ be able to clear a frozen set.
> Hmmm, the problem here, I think, is that tp_clear is
> really only designed for use by the garbage collector.
> Giving anything else access to it is probably wrong.


> Clearability is not a general feature in Python land --
> a few types have a clear() method, but this is an
> ad hoc feature of the type concerned. I don't think
> it makes sense to have a general PyObject_Clear
> function at all.

I'm thinking the same thing, which is why I'm now favoring PySet_Clear()


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