[Numpy-discussion] IndexExpression bug?
Robert Kern
robert.kern@gmail....
Fri Jun 5 17:12:02 CDT 2009
On Fri, Jun 5, 2009 at 16:14, Michael McNeil Forbes
<mforbes@physics.ubc.ca> wrote:
> >>> np.array([0,1,2,3])[1:-1]
> array([1, 2])
>
> but
>
> >>> np.array([0,1,2,3])[np.s_[1:-1]]
> array([1, 2, 3])
> >>> np.array([0,1,2,3])[np.index_exp[1:-1]]
> array([1, 2, 3])
>
> Possible fix:
> class IndexExpression(object):
> ...
> def __len__(self):
> return 0
>
> (Presently this returns sys.maxint)
>
> Does this break anything (I can't find any coverage tests)? If not, I
> will submit a ticket.
I think that getting rid of __getslice__ and __len__ should work
better. I don't really understand what the logic was behind including
them in the first place, though. I might be missing something.
In [21]: %cpaste
Pasting code; enter '--' alone on the line to stop.
:class IndexExpression(object):
: """
: A nicer way to build up index tuples for arrays.
:
: For any index combination, including slicing and axis insertion,
: 'a[indices]' is the same as 'a[index_exp[indices]]' for any
: array 'a'. However, 'index_exp[indices]' can be used anywhere
: in Python code and returns a tuple of slice objects that can be
: used in the construction of complex index expressions.
: """
:
: def __init__(self, maketuple):
: self.maketuple = maketuple
:
: def __getitem__(self, item):
: if self.maketuple and type(item) is not tuple:
: return (item,)
: else:
: return item
:--
In [22]: s2 = IndexExpression(False)
In [23]: s2[1:-1]
Out[23]: slice(1, -1, None)
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
-- Umberto Eco
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