(Adding python-dev, keeping python-list)
> Quoth Robin Thomas <robin.thomas@starmedia.net>:
> | Using Python 2.0 on Win32. Am I the only person to be depressed by the
> | following behavior now that __getitem__ does the work of __getslice__?
> |
> | Python 2.0 (#8, Oct 16 2000, 17:27:58) [MSC 32 bit (Intel)] on win32
> | >>> d = {}
> | >>> d[0:1] = 1
> | >>> d
> | {slice(0, 1, None): 1}
> |
> | And then, for more depression:
> |
> | >>> d[0:1] = 2
> | >>> d
> | {slice(0, 1, None): 1, slice(0, 1, None): 2}
> |
> | And then, for extra extra chagrin:
> |
> | >>> print d[0:1]
> | Traceback (innermost last):
> | File "<pyshell#11>", line 1, in ?
> | d[0:1]
> | KeyError: slice(0, 1, None)
>
> If it helps, you ruined my day.
Mine too. :-)
> | So, questions:
> |
> | 1) Is this behavior considered a bug by the BDFL or the community at large?
I can't speak for the community, but it smells like a bug to me.
> | If so, has a fix been conceived? Am I re-opening a long-resolved issue?
No, and no.
> | 2) If we're still open to proposed solutions, which of the following do you
> | like:
> |
> | a) make slices hash and cmp as their 3-tuple (start,stop,step),
> | so that if I accidentally set a slice object as a key,
> | I can at least re-set it or get it or del it :)
Good idea. The SF patch manager is always open.
> | b) have dict.__setitem__ expressly reject objects of SliceType
> | as keys, raising your favorite in (TypeError, ValueError)
This is *also* a good idea.
> From: Donn Cave <donn@oz.net>
>
> I think we might be able to do better. I hacked in a quick fix
> in ceval.c that looks to me like it has the desired effect without
> closing the door to intentional slice keys (however unlikely.)
[...]
> *** Python/ceval.c.dist Thu Feb 1 14:48:12 2001
> --- Python/ceval.c Wed Feb 28 21:52:55 2001
> ***************
> *** 3168,3173 ****
> --- 3168,3178 ----
> /* u[v:w] = x */
> {
> int ilow = 0, ihigh = INT_MAX;
> + if (u->ob_type->tp_as_mapping) {
> + PyErr_SetString(PyExc_TypeError,
> + "dict object doesn't support slice assignment");
> + return -1;
> + }
> if (!_PyEval_SliceIndex(v, &ilow))
> return -1;
> if (!_PyEval_SliceIndex(w, &ihigh))
Alas, this isn't right. It defeats the purpose completely: the whole
point was that you should be able to write a sequence class that
supports extended slices. This uses __getitem__ and __setitem__, but
class instances have a nonzero tp_as_mapping pointer too!
--Guido van Rossum (home page: http://www.python.org/~guido/)
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