[Numpy-discussion] Thoughts on an ndarray super-class
oliphant.travis at ieee.org
Wed Feb 22 23:46:04 EST 2006
>On 2/23/06, Travis Oliphant <oliphant.travis at ieee.org> wrote:
>>I have been thinking, however, of replacing it with a super-class that
>>does not define the dimensions or strides.
>Having a simple 1-d array in numpy would be great. In an ideal world
>I would rather see a 1-d array implemented in C together with a set of
>array operations that is rich enough to allow trivial implementation
>of ndarray in pure python.
You do realize that this is essentially numarray, right? And your dream
of *rich enough* 1-d operations to allow *trivial* implementation may be
a bit far-fetched, but I'm all for dreaming.
>When you say "does not define the dimensions or strides" do you refer
>to python interface or to C struct? I thought python did not allow to
>add data members to object structs in subclasses.
Yes, you can add data-members to object structs in sub-classes. Every
single Python Object does it. The standard Python Object just defines
PyObject_HEAD or PyObject_VAR_HEAD.
This is actually the essence of inheritance in C and it is why
subclasses written in C must have compatible memory layouts. The first
part of the C-structure must be identical, but you can add to it all you
It all comes down to: Can I cast to the base-type C-struct and have
everything still work out when I dereference a particular field?
This will be true if PyArrayObject is
I suppose we could change the
and place it in the PyBaseArrayObject where it would be used as a length
But, I don't really like that...
>>In other words, the default array would be just a block of memory. The
>>standard array would inherit from the default and add dimension and
>If python lets you do it, how will that block of memory know its size?
It won't of course by itself unless you add an additional size field.
Thus, I'm not really sure whether it's a good idea or not. I don't
like the idea of adding more and more fields to the basic C-struct that
has been around for 10 years unless we have a good reason. The other
issue is that the data-pointer doesn't always refer to memory that the
ndarray has allocated, so it's actually incorrect to think of the
ndarray as both the block of memory and the dimensioned indexing.
The memory pointer is just that (a memory pointer). We are currently
allowing ndarray's to create their own memory but that could easily
change so that they always use some other object to allocate memory.
In short, I don't see how to really do it so that the base object is
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