8000 can't index string- and unicode- numpy-scalars with an empty tuple · Issue #7267 · numpy/numpy · GitHub
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ahaldane opened this issue Feb 17, 2016 · 4 comments
Open

can't index string- and unicode- numpy-scalars with an empty tuple #7267

ahaldane opened this issue Feb 17, 2016 · 4 comments
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@ahaldane
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As discovered in #7259 and #7260, string- and unicode- numpy scalars do not support indexing with an empty tuple, unlike other scalars:

>>> numpy.string_("ABC")[()]
TypeError: string indices must be integers, not tuple
>>> numpy.int32(1)[()]
1

This may be a problem because indexing with an empty tuple is a way of converting possible 0-d arrays to scalars:

>>> a = numpy.int64(1)
>>> b = numpy.array(a)
>>> type(a[()]), type(b[()])
(numpy.int64, numpy.int64)

As of writing this it's not 100% clear to me we actually want this. It could be that instead of just writing

return possiblearr[()]

we should encourage people to write something like

if isinstance(possiblearr, ndarray):
    return possiblearr[()]
return possiblearr

But, on the other hand it's probably a good idea for all scalar types to behave similarly. I made a rough outline for a fix in a comment in #7260.
@ahaldane ahaldane mentioned this issue Feb 22, 2016
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This was referenced Apr 29, 2016
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@ahaldane ahaldane mentioned this issue Oct 14, 2016
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@ahaldane ahaldane mentioned this issue Feb 28, 2017
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@eric-wieser
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Related: numpy.string_("ABC")[...] fails in the same way

@charris
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charris commented Mar 6, 2017

OTOH,

In [5]: numpy.string_("ABC")[1]
Out[5]: 'B'

@eric-wieser
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This manifests itself in np.ma.array(['ab', 'cd']).take(1) due to the patch in #7586

@eric-wieser
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Arguably not a bug - we're never going to have this work on object scalars, so having it fail on string scalars too forces the library writer to use a solution that works for object scalars too.

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