[Numpy-discussion] Recarray attributes writeable (original) (raw)

Andrew Straw strawman at astraw.com
Fri Jun 16 17:46:19 EDT 2006

Erin Sheldon wrote:

Anyway - Recarrays have convenience attributes such that fields may be accessed through "." in additioin to the "field()" method. These attributes are designed for read only; one cannot alter the data through them. Yet they are writeable:

tr=numpy.recarray(10, formats='i4,f8,f8', names='id,ra,dec') tr.field('ra')[:] = 0.0 tr.ra

array([ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.]) tr.ra = 3 tr.ra 3 tr.field('ra') array([ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.]) I feel this should raise an exception, just as with trying to write to the "size" attribute. Any thoughts? I have not used recarrays much, so take this with the appropriate measure of salt.

I'd prefer to drop the entire pseudo-attribute thing completely before it gets entrenched. (Perhaps it's too late.)

I've used a similar system in pytables which, although it is convenient in the short term and for interactive use, there are corner cases that result in long term headaches. I think you point out one such issue for recarrays. There will be more. For example:

In [1]:import numpy

In [2]:tr=numpy.recarray(10, formats='i4,f8,f8', names='id,ra,dec')

In [3]:tr.field('ra')[:] = 0.0

In [4]:tr.ra Out[4]:array([ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.])

In [5]:del tr.ra

exceptions.AttributeError Traceback (most recent call last)

/home/astraw/

AttributeError: 'recarray' object has no attribute 'ra'

The above seems completely counterintuitive -- an attribute error for something I just accessed? Yes, I know what's going on, but it certainly makes life more confusing than it need be, IMO.

Another issue is that it is possible to have field names that are not valid Python identifier strings.

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