[Numpy-discussion] Simplest ndarray subclass __new__ possible?
zpincus at stanford.edu
Tue Feb 28 01:28:04 EST 2006
I think I'm getting a hold on most of what's going on. The
__array_priority__ bit remains a bit opaque (can anyone offer
guidance?), and I still have some questions about why the __new__ of
the matrix subclass ha so much complexity.
> So, if you over-write the __new__ constructor for your class and
> want to call the ndarray.__new__ constructor you have to realize
> that you need to think of what you are doing in terms of "wrapping"
> some other created piece of memory or "initializing your memory".
This makes good sense.
> If you want your array to be-able to "convert" arbitrary objects to
> arrays, instead, then your constructor could in-fact be as simple as
> class myarray(numpy.ndarray):
> def __new__(cls, obj):
> return numpy.array(obj).view(cls)
However, the matrix class's __new__ has a lot more complexity. Is
*all* of the complexity there in the service of ensuring that
matrices are only 2d? It seems like there's more going on there than
> Then, if you want, you can define an __init__ method to handle
> setting of attributes --- however, if you set some attributes, then
> you need to think about what you want to happen when your new array
> gets "sliced" or added to. Because the internal code will create
> your new array (without calling new) and then call
> __array_finalize__(self, parent)
> where parent could be None (if there is no parent --- i.e. this is
> a new array).
> Any attributes you define should also be defined here so they get
> passed on to all arrays that are created..
All of this also makes sense.
> I hope this helps some.
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