[Python-Dev] Fixing _PyEval_SliceIndex so that integer-like objects can be used
Hello again, There is a great discussion going on the numpy list regarding a proposed PEP for multidimensional arrays that is in the works. During this discussion as resurfaced regarding slicing with objects that are not IntegerType objects but that have a tp_as_number-nb_int method to convert to an int. 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. If this is acceptable, it is an easy patch. Thanks, -Travis Oliphant ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Fixing _PyEval_SliceIndex so that integer-like objects can be used
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). -- --Guido van Rossum (home page: http://www.python.org/~guido/) ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Fixing _PyEval_SliceIndex so that integer-like objects can be used
Travis Oliphant wrote: Hello again, There is a great discussion going on the numpy list regarding a proposed PEP for multidimensional arrays that is in the works. During this discussion as resurfaced regarding slicing with objects that are not IntegerType objects but that have a tp_as_number-nb_int method to convert to an int. 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. You would also have to change apply_slice() since that also has a guard for checking the slice arguments are either NULL, int, or long objects. But I am +1 with it since the guard is already there for ints and longs to handle those properly and thus the common case does not slow down in any way. As long as it also accepts Python objects that define __int__ and not just C types that have the nb_int slot defined I am okay with this idea. -Brett ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Fixing _PyEval_SliceIndex so that integer-like objects can be used
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. ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Fixing _PyEval_SliceIndex so that integer-like objects can be used
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 ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Fixing _PyEval_SliceIndex so that integer-like objects can be used
Guido van Rossum 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, O.K., then how about if arrayobjects can make it in the core, then a check for a rank-0 integer-type arrayobject is allowed before raising an exception? -Travis ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
