Subclassing numpy ndarray breaks at getitem

Question

A very very basic ndarraysubclass (which doesn't do anything yet) is laid out below. However the print function (or better, __getitem__()) doesn't work.

class imarray(np.ndarray):
    def __new__(subtype, shape, dtype=float, buffer=None, offset=0,
          strides=None, order=None):

        # It also triggers a call to InfoArray.__array_finalize__
        obj = np.ndarray.__new__(subtype, shape, dtype, buffer, offset, strides,
                         order)
        return obj

    def __getitem__(self, key):
        return np.ndarray.__getitem__(key)





y = imarray((2,3))
x = np.ndarray((2,3))
print(x)
print(y)

x is shown correctly (and as expected the 6 values are random). However the print y (or print(y[0,0])) returns the following error:

return np.ndarray.__getitem__(key) 
TypeError: descriptor __getitem__ requires a 'numpy.ndarray' object but received a 'int'

So how do I subclass correctly (and catch the set/getitem)

Antti Haapala · Accepted Answer · 2015-03-30 13:49:07Z

4

You must pass the self too, either

return np.ndarray.__getitem__(self, key)

or

return super(imarray, self).__getitem__(key)

edited Mar 30, 2015 at 13:49

answered Mar 30, 2015 at 13:24

Antti Haapala

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1 Comment

paul23 Over a year ago

@not doing anything, I removed the "doing" for the sake of providing the minimal example.

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