Defining custom types
oliphant.travis at ieee.org
Fri Oct 27 15:02:56 CDT 2006
Jonathan Wang wrote:
> On 10/27/06, *Travis Oliphant* <oliphant.travis at ieee.org
> <mailto:oliphant.travis at ieee.org>> wrote:
> > If I redefine the string function, I encounter another, perhaps more
> > serious problem leading to a segfault. I've defined my string
> > to be extremely simple:
> > >>> def printer(arr):
> > ... return str(arr)
> > Now, if I try to print an element of the array:
> > >>> mxArr
> > I get to this stack trace:
> > #0 scalar_value (scalar=0x814be10, descr=0x5079e0) at
> > scalartypes.inc.src:68
> > #1 0x0079936a in PyArray_Scalar (data=0x814cf98, descr=0x5079e0,
> > base=0x814e7a8) at arrayobject.c:1419
> > #2 0x007d259f in array_subscript_nice (self=0x814e7a8,
> > at arrayobject.c:1985
> > #3 0x00d17dde in PyObject_GetItem (o=0x814e7a8, key=0x804eb8c) at
> > Objects/abstract.c:94
> > (Note: for some reason gdb claims that arrayobject.c:1985 is
> > array_subscript_nice, but looking at my source this line is
> > in array_item_nice. *boggle*)
> > But scalar_value returns NULL for all non-native types. So,
> destptr in
> > PyArray_Scalar is set to NULL, and the call the copyswap segfaults.
> > Perhaps scalar_value should be checking the scalarkind field of
> > PyArray_Descr, or using the elsize and alignment fields to
> figure out
> > the pointer to return if scalarkind isn't set?
> Hmmm... It looks like the modifications to scalar_value did not take
> into account user-defined types. I've added a correction so that
> user-defined types will use setitem to set the scalar value into the
> array. Presumably your setitem function can handle setting the array
> with scalars of your new type?
> I've checked the changes into SVN.
> Do there also need to be changes in scalartypes.inc.src to use getitem
> if a user-defined type does not inherit from a Numpy scalar?
This needs to be clarified. I don't think it's possible to do it
without inheriting from a numpy scalar at this point (the void numpy
scalar can be inherited from and is pretty generic). I know I was not
considering that case when I wrote the code.
> i.e. at scalartypes.inc.src:114 we should return some pointer
> calculated from the PyArray_Descr's elsize and alignment field to get
> the destination for the "custom scalar" type to be copied.
I think this is a good idea. I doubt it's enough to fix all places that
don't inherit from numpy scalars, but it's a start.
It seems like we need to figure out where the beginning of the data is
for the type which is assumed to be defined on alignment boundaries
after a PyObject_HEAD (right)? This could actually be used for
everything and all the switch and if statements eliminated.
I think the alignment field is the only thing needed, though. I don't
see how I would use the elsize field?
> As it stands, if the user-defined type does not inherit from a Numpy
> scalar, lots of things continue to break.
Not surprising, I did not make sure and support this.
> Furthermore it seems like the scalar conversions prefer the builtin
> types, but it seems to me that the user-defined type should be preferred.
I'm not sure what this means.
> i.e. if I try to get an element from my mxDateTime array, I get a
> float back:
> >>> mxArr = DateTime.now()
> >>> mxArr
Why can you index mxArr? What is mxArr? If it's a scalar, then
why can you index it? What is type(mxArr)?
> But what I really want is the mxDateTime, which, oddly enough, is what
> happens if I use tolist():
> >>> mxArr.tolist()
> [<DateTime object for '2006-10-27 14:33:57.25' at a73c60>]
That's not surprising because tolist just calls getitem on each element
in the array to construct the list.
Using Tomcat but need to do more? Need to support web services, security?
Get stuff done quickly with pre-integrated technology to make your job easier
Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo
More information about the Numpy-discussion