[Numpy-discussion] Re: change in semantics of arange?

[Todd Miller]

On Fri, 2003-05-16 at 13:03, Paul Dubois wrote:
> C:\numpy\numarray\Packages\MA2>python
> Python 2.3b1 (#40, Apr 25 2003, 19:06:24) [MSC v.1200 32 bit (Intel)] on
> win32
> Type "help", "copyright", "credits" or "license" for more information.
> >>> import numarray
> >>> x=numarray.arange(5,3,2)
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
>   File "c:\python23\Lib\site-packages\numarray\numarray.py", line 924, in
> arange
>     r = _fillarray(size, start, stride, type)
>   File "c:\python23\Lib\site-packages\numarray\numarray.py", line 120, in
> _fillarray
>     outarr = NumArray((size,), outtype)
> libnumarray.error: NA_updateDataPtr: error getting read buffer data ptr
> >>> import Numeric
> >>> Numeric.arange(5,3,2)
> zeros((0,), 'l')
> >>>
> 
> Is this change intentional?

No.  It's bugs in arange and also the memory object which are creating a
negative length buffer.  The buffer API then reports a negative length
which is fortuitously interpreted as an error.  Ya gotta smile...

It's fixed in CVS.  I modified the memory module so that:

>>> import memory
>>> memory.new_memory(-10)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
ValueError: new_memory: invalid region size: -10.

And I modified arange so that negative sizes are clipped to 0.  So now:

>>> import numarray
>>> numarray.arange(5,3,2)
array([])


> 
-- 
Todd Miller 			jmiller at stsci.edu
STSCI / ESS / SSB