[Numpy-discussion] Re: Problem with _wrapit

[Tim Hochberg]

Well, I got no negative opinions (no opinions at all for that matter), 
so I went ahead and commited this change (with test cases -- thanks for 
the push Albert).

-tim



Tim Hochberg wrote:

>
> There's a problem with the _wrapit function. If the function that it 
> wraps, returns  a scalar, it blows up. Here's an example:
>
>    import numpy
>
>    class narray(numpy.ndarray):
>        def get_argmax(self):
>            raise AttributeError
>        argmax = property(get_argmax)
>              a = narray([3], int, numpy.arange(3))
>    print type(a), isinstance(a, numpy.ndarray)
>
>    print a
>    print numpy.argmax(a)
>
> ==>
>
>    <class '__main__.narray'> True
>    [0 1 2]
>    Traceback (most recent call last):
>      File "find_bug.py", line 13, in ?
>        print numpy.argmax(a)
>      File "C:\python24\lib\site-packages\numpy\core\oldnumeric.py",
>    line 278, in argmax
>        return _wrapit(a, 'argmax', axis)
>      File "C:\python24\lib\site-packages\numpy\core\oldnumeric.py",
>    line 170, in _wrapit
>        result = wrap(result)
>    TypeError: can only be called with ndarray object
>
>
> A possible fix is to do another isinstance check on the way out:
>
>    def _wrapit(obj, method, *args, **kwds):
>        try:
>            wrap = obj.__array_wrap__
>        except AttributeError:
>            wrap = None
>        result = getattr(asarray(obj),method)(*args, **kwds)
>        if wrap and isinstance(result, mu.ndarray):
>            result = wrap(result)
>        return result
>
> That fixes this problem, and I think it should be OK in general, but 
> I'd like a second opinion before comitting it.
>
> regards,
>
> -tim
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