[Numpy-discussion] Example of power of new data-type descriptors.

dHering vel.accel at gmail.com
Wed Dec 28 16:42:08 CST 2005


[Sorry for the mis-post]

Hi Travis,

I really hope that the future brings Scipy and Pytables together.
Thank you very much for your contributions and motivation Travis.

Dieter Hering


On 12/28/05, dHering <vel.accel at gmail.com> wrote:
> On 12/26/05, Travis Oliphant <oliphant.travis at ieee.org> wrote:
> >
> >
> > I'd like more people to know about the new power that is in scipy core
> > due to the general data-type descriptors that can now be used to define
> > numeric arrays.  Towards that effort here is a simple example (be sure
> > to use latest SVN -- there were a coupld of minor changes that improve
> > usability made recently).  Notice this example does not use a special
> > "record" array subclass.  This is just a regular array.  I'm kind of
> > intrigued (though not motivated to pursue) the possibility of accessing
> > (or defining) databases directly into scipy_core arrays using the record
> > functionality.
> >
> > # Define a new data-type descriptor
> >  >>> import scipy
> >
> >  >>> dtype = scipy.dtypedescr({'names': ['name', 'age', 'weight'],
> > 'formats': ['S30', 'i2', 'f4']})
> >  >>> a = scipy.array([('Bill',31,260),('Fred',15,135)], dtype=dtype)
> > # the argument to dtypedescr could have also been placed here as the
> > argument to dtype
> >
> >  >>> print a['name']
> > [Bill Fred]
> >
> >  >>> print a['age']
> > [31 15]
> >
> >  >>> print a['weight']
> > [ 260.  135.]
> >
> >  >>> print a[0]
> > ('Bill', 31, 260.0)
> >
> >  >>> print a[1]
> > ('Fred', 15, 135.0)
> >
> > It seems to me there are some very interesting possibilities with this
> > new ability.  The record array subclass adds an improved scalar type
> > (the record) and attribute access to get at the fields:  (e.g.  a.name,
> > a.age, and a.weight).    But, if you don't need attribute access you can
> > use regular arrays to do a lot of what you might need a record array to
> > accomplish for you.  I'd love to see what people come up with using this
> > new facility.
> >
> > The new array PEP for Python basically proposes adding a very simple
> > array object (just the basic PyArrayObject * of Numeric with a
> > bare-bones type-object table) plus this new data-type descriptor object
> > to Python and a very few builtin data-type descriptors (perhaps just
> > object initially).   This would basically add the array interface to
> > Python directly and allow people to start using it generally.  The PEP
> > is slow going because it is not on my priority list right now because it
> > is not essential to making scipy_core work well.  But, I would love to
> > have more people ruminating on the basic ideas which I think are
> > crystallizing.
> >
> > Best wishes for a new year,
> >
> > -Travis Oliphant
> >
> >
> >
> >
> >
> >
> >
> >
> >
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