[Numpy-discussion] numpy C API bugs?

David Ian Brown dbrown at ucar.edu
Fri Mar 10 11:52:07 CST 2006


Hi Travis,
Yes, now I see that I just wasn't looking closely enough at the the  
docs, that Numeric's getitem did have only
one argument, and the docs have the arguments in the correct order both  
for the function and the macro.
I was just confused by the fact that the macro has the arguments in the  
opposite order of the function.
So the only problem was the missing 'f' in the macro.
  -dave
On Mar 9, 2006, at 10:28 PM, Travis Oliphant wrote:

> David Ian Brown wrote:
>>>
>>> I have recently been engaged in updating the PyNIO module  
>>> (http://www.pyngl.ucar.edu/Nio.html)
>>> to work with the NumPy C API. It was originally coded using the  
>>> Numeric's C API.
>>>
>>> In the process I have encountered what appear to me to be a couple  
>>> of  bugs in the interface.  They were relatively minor  and not   
>>> difficult to work around, but you would probably like to know of  
>>> them if you don't already.
>>>
>>> In the NumPy version of arrayobject.h the macros PyArray_GETITEM and  
>>> PyArray_SETITEM
>>> are defined in way that does not work.  Here is the GETITEM macro:
>>>
>>>  #define PyArray_GETITEM(obj,itemptr)                    \
>>>        ((char *)itemptr,       \
>>>                                           (PyArrayObject *)obj);
>>>
>
> Thank you very much for catching this.  The introduction of 'f' was  
> more recent then the writing of these macros and so this error crept  
> in.    I'm definitely glad to fix it.
>
>> Correction: actually "Guide to NumPy" has the 'getitem' function  
>> documented with the arguments ordered
>> as  implemented in NumPy (but still opposite from Numeric). Only the  
>> macro is documented opposite from
>> its implementation.
>
> I think further clarification is needed.
> First of all Numeric did not have macros.  They just had function  
> pointers to getitem. Second, Numpy's function pointers to getitem and  
> setitem are almost exactly the same.  The only difference is the  
> *addition* of another argument to both functions to allow the array to  
> be passed in (so that the size of the array and whether or not it's  
> well-behaved can be known).
> So, the order is *not* different in NumPy and Numeric, there is just  
> another argument needed.
> The new macros introduced do have a different order (and I don't think  
> it's documented oppositely --- it's perhaps not documented well at  
> all, however :-) and so may be confusing).
>
> It is recommended to use the macros.  They are
>
> PyArray_GETITEM(array, itemptr)
>
> Return a Python object corresponding to the item in the array at the  
> location itemptr.
>
> PyArray_SETITEM(array, itemptr, obj)
>
> Set object into the array at the memory pointed to by itemptr (an  
> attempt is made to convert to the right type if that is possible).
>
> Thanks for the report.
>
> -Travis
>
>
>
>
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