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Thu Aug 17 07:57:54 CEST 2006 · https://mail.python.org/pipermail/python-dev/2006-August/068328.html

On 8/16/06, Phillip J. Eby <pje at telecommunity.com> wrote:
>
> It seems to me that you could drop the FAST_SUBCLASS bit, since none of the
> other bits will be set if it is not a subclass of a builtin.  That would
> free up one flag bit -- perhaps usable for that BaseException flag Guido
> wants.  :)

:-)  Right, I'm not using the bit currently.  I was thinking that it
would be interesting to change the CheckExact versions to also use
this.  It's a little more work, but you lose the second comparison for
Check.  I expect that it would be slower, but I was just curious.

So with the patch we currently have:

#define PyInt_CheckExact(op) ((op)->ob_type == &PyInt_Type)
#define PyInt_Check(op) (PyInt_CheckExact(op) || \
                 PyType_FastSubclass((op)->ob_type, Py_TPFLAGS_INT_SUBCLASS))

But we could have something like:

#define PyInt_CheckExact(op) (PyType_FastClass(op,Py_TPFLAGS_INT_CLASS))
#define PyInt_Check(op) (PyType_FastSubclass(op,Py_TPFLAGS_INT_SUBCLASS))

It would change the CheckExact()s from: op->ob_type ==
global-variable, to: op->ob_type & CONSTANT == CONSTANT.  Check would
be the same as the CheckExact, just with different constants.  The
Check version would then drop the || condition.

I might play with this at the sprint next week.  It does seem to make
sense to do BaseException too.  It will take 4 or 5 bits to handle the
current ones plus BaseException, which we can easily spare in
tp_flags.

n

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[Python-Dev] Type of range object members