I am trying to create a subclass of ndarray that has additional attributes. These attributes are maintained with most numpy functions if __array_finalize__ is used. The main exception I have found is concatenate (and hstack/vstack, which just wrap concatenate). In this case, __array_finalize__ is passed an array that has already been stripped of the additional attributes, and I don't see a way to recover this information. In my particular case at least, there are clear ways to handle corner cases (like being passed a class that lacks these attributes), so in principle there no problem handling concatenate in a general way, assuming I can get access to the attributes. So is there any way to subclass ndarray in such a way that concatenate can be handled properly? I have been looking extensively online, but have not been able to find a clear answer on how to do this, or if there even is a way.