On So, 2015-08-30 at 21:09 -0700, Jaime Fernández del Río wrote: > There's been some work going on recently on Py2 vs Py3 object > comparisons. If you want all the background, see gh-6265 and follow > the links there. > > > There is a half baked PR in the works, gh-6269, that tries to unify > behavior and fix some bugs along the way, by replacing all 2.x uses of > PyObject_Compare with several calls to PyObject_RichCompareBool, which > is available on 2.6, the oldest Python version we support. > > > The poster child for this example is computing np.sign on an object > array that has an np.nan entry. 2.x will just make up an answer for > us: > > > >>> cmp(np.nan, 0) > -1 > > > even though none of the relevant compares succeeds: > > > >>> np.nan < 0 > False > >>> np.nan > 0 > > False > >>> np.nan == 0 > > False > > > The current 3.x is buggy, so the fact that it produces the same made > up result as in 2.x is accidental: > > > >>> np.sign(np.array([np.nan], 'O')) > array([-1], dtype=object) > > > Looking at the code, it seems that the original intention was for the > answer to be `0`, which is equally made up but perhaps makes a little > more sense. > > > There are three ways of fixing this that I see: > 1. Arbitrarily choose a value to set the return to. This is > equivalent to choosing a default return for `cmp` for > comparisons. This preserves behavior, but feels wrong. > 2. Similarly to how np.sign of a floating point array with nans > returns nan for those values, return e,g, None for these > cases. This is my preferred option.
That would be my gut feeling as well. Returning `NaN` could also make sense, but I guess we run into problems since we do not know the input type. So `None` seems like the only option here I can think of right now. - Sebastian > 1. Raise an error, along the lines of the TypeError: unorderable > types that 3.x produces for some comparisons. > Thoughts anyone? > > > Jaime > -- > > (\__/) > ( O.o) > ( > <) Este es Conejo. Copia a Conejo en tu firma y ayúdale en sus > planes de dominación mundial. > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion
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