numpy.dtype.subdtype
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dtype.subdtype
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Tuple (item_dtype, shape)if thisdtypedescribes a sub-array, and None otherwise.The shape is the fixed shape of the sub-array described by this data type, and item_dtype the data type of the array. If a field whose dtype object has this attribute is retrieved, then the extra dimensions implied by shape are tacked on to the end of the retrieved array. 
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Licensed under the NumPy License.
    https://docs.scipy.org/doc/numpy-1.11.0/reference/generated/numpy.dtype.subdtype.html