Re: [Numpy-discussion] C Api newbie question

[Matt K. <mat...@ho...>]

>>Matt Knox wrote:>>> Hi there. I'm in the unfortunate situation of trying =
to track down a >> memory error in someone elses code, and to make matters =
worse I don't >> really know jack squat about C programming. The problem se=
ems to arise >> when several numpy arrays are created from C arrays in the =
C api and >> returned to python, and then trying to print out or cast to a =
string >> the resulting array. I think the problem may be happening due to =
the >> following chunk of code:>> {>>      PyObject* temp =3D PyArray_Simpl=
eNewFromData(1, &numobjs, typeNum, >> dbValues);>>      PyObject* temp2 =3D=
 PyArray_FromArray((PyArrayObject*)temp, >> ((PyArrayObject*)temp)->descr, =
DEFAULT_FLAGS | ENSURECOPY);>>      Py_DECREF(temp);>>      PyDict_SetItemS=
tring(returnVal, "data", temp2);>>      Py_DECREF(temp2);>> }>>  >> Lets as=
sume that all my other inputs up this point are fine and that >> numobjs, t=
ypeNum, and dbValues are fine. Is their anything obviously >> wrong with th=
e above chunk of code? or does it appear ok? Ultimately >> the dictionary "=
returnVal" is returned by the function this code came >> from, and everythi=
ng else is discarded. Any help is very greatly >> appreciated. Thanks in ad=
vance,
> You didn't indicate what kind of trouble you are having.>> First of all, =
this is kind of odd style.  Why is a new array created > from a data-pointe=
r and then copied using PyArray_FromArray (the > ENSURECOPY flag will give =
you a copy)?  Using>> temp2 =3D PyArray_Copy(temp)>> seems simpler.   This =
will also avoid the reference-count problem that > is currently happening i=
n the PyArray_FromArray call on the descr > structure.    Any array-creatio=
n function that takes a descr structure > "steals" a reference to it, so yo=
u need to increment the reference count > if you are passing an unowned ref=
erence to a ->descr structure.>> -Travis
=20
Sorry. Yeah, the problem was the interpreter crashing on exit, which aftery=
our response definitely seems like it was a reference count issue. Ichanged=
 the PyArray_FromArray call to be PyArray_Copy and it seems to workfine. Th=
ank you very much!
=20
Love the numpy stuff (when I can stay in the python world and not mess with=
the C stuff :) ). Keep up the great work!
=20
- Matt
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