[SciPy-user] C++ extensions

David Grant david at dwavesys.com
Mon Nov 8 19:04:55 CST 2004

Prabhu Ramachandran wrote:

>>>>>>"DG" == David Grant <david.grant at telus.net> writes:
>    DG> I looked at some Weave information, but that didn't help,
>    DG> because I obviously can't run this in-line since it is many
>    DG> files.
>That seems like an incorrect assumption.  Weave will let you call any
>function you want from within the inlined code.  From the information
>you have provided, I assume you want to do something like this in
> a = Numeric.array(...)
> # Setup your matrix the way you want.
> call_c_code_that_does_stuff_to_array(a)
> # Continue work from Python...
>So simply define call_c_code_that_does_stuff_to_array and write some
>simple C++ code that does what you want.  This is definitely doable
>from weave.  The question is what 'output' does your blackbox produce?
>If its a number/array then they are easy to handle since weave will
>let you do that.  When you call inline you can pass headers and link
>to libraries that you have built.  So in theory you can build your
>blackbox C++ code as a library, and call its functions from your
>inlined code.

I tried doing what you describe.  I basically am doing the following as 
a test to see if I can get this to work.  I have the following test 
python script:

import weave
inc_dirs=['/home/david/working_dir/python/qcd', '/usr/include']
lib_dirs=['/home/david/working_dir/python/qcd', '/usr/lib']
code = """
#include "DComplex.h"
DComplex z(2,3);
weave.inline(code, include_dirs=inc_dirs, library_dirs=lib_dirs, 
libraries=libs, verbose=2)

DComplex.cpp and DComplex.h define a class for complex numbers.  I build 
DComplex.cpp separately using a makefile. This does:

gcc -c DComplex.cpp
ar rc libdcomplex.a DComplex.o
ranlib libdcomplex.a

This builds a static library libdcomplex.a  Then, as shown in my test 
python script above, I use libs=['dcomplex'] and that will include 
libdcomplex.a in the current directory.  The linking actually seems to 
work ok!  The prooblem seems to be when python imports the file:

running build_ext
customize UnixCCompiler
customize UnixCCompiler using build_ext
building 'sc_89dfe56fc9f6dd6ee19b60174c27c7511' extension
compiling C++ sources
g++ options: '-fno-strict-aliasing -DNDEBUG -fPIC'
compile options: '-I/home/david/working_dir/python/qcd -I/usr/include 
-I/usr/lib/python2.3/site-packages/weave/scxx -I/usr/include/python2.3 -c'
g++: /home/david/.python23_compiled/sc_89dfe56fc9f6dd6ee19b60174c27c7511.cpp
g++ -pthread -shared 
-L/home/david/working_dir/python/qcd -L/usr/lib -ldcomplex -o 

Traceback (most recent call last):
  File "test_weave.py", line 20, in ?
    weave.inline(code,['arr','_Narr'], include_dirs=inc_dirs, 
library_dirs=lib_dirs, libraries=libs, verbose=2)
  File "/usr/lib/python2.3/site-packages/weave/inline_tools.py", line 
335, in inline
    auto_downcast = auto_downcast,
  File "/usr/lib/python2.3/site-packages/weave/inline_tools.py", line 
445, in compile_function
    exec 'import ' + module_name
  File "<string>", line 1, in ?
undefined symbol: _ZZ13compiled_funcP7_objectS0_EN8DComplexC1Edd

As you can see above there is an undefined symbol in the python .so 
extension, which ends in ...DComplex...

I've been stuck on this for an hour and I have no clue what is wrong.  
If you or anything else can help me, it would be appreciated.

>Of course, you can use SWIG or Boost.Python also.  But weave is still
>an option.
>SciPy-user mailing list
>SciPy-user at scipy.net

David J. Grant
Scientific Officer
Intellectual Property
D-Wave Systems Inc.
tel: 604.732.6604
fax: 604.732.6614


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