The __index__ method returns an integer from an array. The current behavior follows the idea of "return an integer if there is 1-element in the array" Your suggestion is to only return an integer if it is a rank-0 array, otherwise raise an error. This could potentially be changed in NumPy 2.0. I'm +0 on the suggestion. -Travis On Oct 27, 2010, at 9:34 AM, Francesc Alted wrote:
Hi,
I find this a bit misleading:
a = np.arange(10)
a[np.array(0)] 0
a[np.array([0])] array([0])
a[[0]] array([0])
But, for regular python lists we have:
l = a.tolist()
l[np.array(0)] 0
l[np.array([0])] 0
i.e. indexing with a rank-0 array and a rank-1 array with one single element return the same result, which I find inconsistent with the expected behaviour for this case, i.e.:
l[[0]]
TypeError Traceback (most recent call last)
/tmp/tables-2.2/<ipython console> in <module>()
TypeError: list indices must be integers, not list
The ultimate reason for this behaviour is this:
np.array(0).__index__() 0
np.array([0]).__index__() 0
But I wonder why NumPy needs the latter behaviour, instead of the more logical:
np.array([0]).__index__()
TypeError Traceback (most recent call last)
/tmp/tables-2.2/<ipython console> in <module>()
TypeError: only rank-0 integer arrays can be converted to an index
This inconsistency has indeed introduced a bug in my application and for solving this I'd need something like:
""" def is_idx(index): """Check if an object can work as an index or not."""
if hasattr(index, "__index__"): # Only works on Python 2.5 on if (hasattr(index, "shape") and index.shape == (1,)): return False try: # (as per PEP 357) idx = index.__index__() return True except TypeError: return False
return False """
i.e. for determining if an object can be an index or not, I need to explicitly check for a shape different from (1,), which is unnecessarily complicated.
So I find the current behaviour prone to introduce errors in apps and I'm wondering why exactly np.array([1]) should work as an index at all. It would not be better if that would raise a ``TypeError``?
Thanks,
-- Francesc Alted _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
--- Travis Oliphant Enthought, Inc. oliphant@enthought.com 1-512-536-1057 http://www.enthought.com