[Numpy-discussion] RFC: out of range slice indexes

Robert Kern robert.kern@gmail....
Mon Jan 14 14:04:20 CST 2008

Neal Becker wrote:
> Robert Kern wrote:
>> Neal Becker wrote:
>>> I've never liked that python silently ignores slices with out of range
>>> indexes.  I believe this is a source of bugs (it has been for me).  It
>>> goes completely counter to the python philosophy.
>>> I vote to ban them from numpy.
>>>>>> from numpy import array
>>>>>> x = array (xrange (10))
>>>>>> x[11]
>>> Traceback (most recent call last):
>>>   File "<stdin>", line 1, in <module>
>>> IndexError: index out of bounds
>>>>>> x[:12] = 2
>>>>>> x
>>> array([2, 2, 2, 2, 2, 2, 2, 2, 2, 2])
>>>>>> len (x)
>>> 10
>>> Silently ignoring the error x[:12] is a bad idea, IMO.  If it meant to
>>> _extend_ x to have lenght 12, at least _that_ would be reasonable (but
>>> I'm not advocating that position).
>>> I believe that out of bounds indexes should always throw IndexError.  We
>>> can't change that in Python now, but maybe we can in numpy.
>> -1. Regardless of the merits if we had a blank slate, there is code that
>> depends on this, specifically my code. It simplifies certain operations
>> that would otherwise need tedious special case-handling.
> For example?

def ichunk(arr, chunk_size=10):
     for i in range(0, len(arr), chunk_size):
         yield arr[i:i+chunk_size]

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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