On Feb 18, 2005, at 4:36 PM, David Ascher wrote:
On Fri, 18 Feb 2005 13:28:34 -0800, Guido van Rossum <[EMAIL PROTECTED]> wrote:Would it be possible to change
_PyEval_SliceIndex in ceval.c
so that rather than throwing an error if the indexing object is not an
integer, the code first checks to see if the object has a
tp_as_number->nb_int method and calls it instead.
I don't think this is the right solution; since float has that method, it would allow floats to be used as slice indices, but that's not supposed to work (to protect yourself against irreproducible results due to rounding errors).
I wonder if floats are the special case here, not "integer like objects".
I've never been particularly happy about the confusion between the two roles of int() and it's C equivalents, i.e. casting and conversion.
All of the __special__ methods for this purpose seem to be usable only for conversion, not casting (__str__, __unicode__, etc.). The only way I've found to pass for a particular value type is to subclass one. We do this a lot in PyObjC.
It ends up being a net win anyway, because you get free implementations of all the relevant methods, at the expense of having two copies of the value. The fact that these proxy objects are no longer visible-from-Python subclasses of Objective-C objects isn't really a big deal in our case, because the canonical Objective-C way to checking inheritance still work. The wrapper types use an attribute protocol for casting (__pyobjc_object__), and delegate to this object with __getattr__.
>>> from Foundation import * >>> one = NSNumber.numberWithInt_(1) >>> type(one).mro() [<class 'objc._pythonify.OC_PythonInt'>, <type 'int'>, <type 'object'>] >>> isinstance(one, NSNumber) False >>> isinstance(one.__pyobjc_object__, NSNumber) True >>> one.isKindOfClass_(NSNumber) 1 >>> type(one) <class 'objc._pythonify.OC_PythonInt'> >>> type(one.__pyobjc_object__) <objective-c class NSCFNumber at 0x300620>
-bob
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