MaskedArray ufuncs don't return out parameter

[ahaldane]

The ufuncs defined for MaskedArrays don't return out if it is supplied as a keyword, unlike normal ufuncs.

>>> a = np.ones(2)
>>> np.add([1,1], 2, out=a) is a
True
>>> np.ma.add([1,1], 2, out=a) is a
False

[mhvk]

I don't think ma ufuncs do anything with out -- in your example, a contains a regular array, while the output is a masked array. Specifically,

ma = np.ma.add([1,1], 2, out=a)
ma.data.base is a
# True

Looking at the code, __array_wrap__ simply views the output of the ufunc (i.e., a) as a MaskedArray and then goes through its logic with the mask. To get this right, one would have to use __array_prepare__ to turn the output array into a masked version before filling it in the calculation.