[Python-Dev] idea for data-type (data-format) PEP

[Alexander Belopolsky]

On Nov 2, 2006, at 8:04 PM, Greg Ewing wrote:

>
> I think the datatype object should almost certainly
> be immutable. Since it's separated from the data
> it's describing, it's possible for one datatype
> object to describe multiple chunks of data. So
> you wouldn't want to mutate one in case it's being
> used for something else that you don't know about.


I only mentioned that the datatype object would be mutable at C level  
because changing the object instead of deleting and creating a new  
one could be a valid optimization in situations where the object is  
know not to be shared.

My main concern was that in ctypes the size of an array is a part of  
the datatype object and this seems to be redundant if used for the  
buffer protocol.  Buffer protocol already reports the size of the  
buffer as a return value of bf_get*buffer methods.

In another post, Greg Ewing wrote:

 > > numpy.array(array.array('d',[1,2,3]))
 > >
 > > and leave-out the buffer object all together.

 > I think the buffer object in his example was just a
 > placeholder for "some arbitrary object that supports
 > the buffer interface", not necessarily another NumPy
 > array.

Yes, thanks. In fact numpy.array(array.array('d',[1,2,3])) already  
works in numpy (I think because numpy knows about the standard  
library array type).  In my example, I wanted to use an object that  
supports buffer protocol and little else.