[Numpy-discussion] Exporting Numpy C functionality to other extension modules

[Todd Miller]

Take a look at the attached extension module "testlite" which 
demonstrates the technique I evolved from this discussion. As we 
discussed,  this usage pattern enables the construction of an extension 
which will take advantage of numarray if it is there,  but will continue 
to work if the user has not installed numarray.  Here's how it works:

1. I created a new API function,  PyArray_isArray() which is safe to 
call in all contexts.  I defined it as:

 #define PyArray_isArray(o) (PyArray_API && NA_isNumArray(o))

I added NA_isNumArray(o) to the numarray C-API because it was the easy 
way  to do it.

2. Ordinary API functions are safe to call once an object has been 
identified to be a numarray because it implies (locally) that the 
PyArray_API pointer has been initialized.

3. I tried out the standard import_array() code and added some cleanup 
for the case where numarray is not installed.  

The only caveat I see at this point is that you are required to include 
numarray headers in order to use this.  In numarray's case,  this might 
necessitate header updates and/or function call modifications.  The 
numarray C-API should stabilize pretty soon,  but I don't think its 
quite there yet.

The same approach should apply to Numeric.

This stuff is in numarray CVS now and should be in the next numarray 
release.

Todd


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