SWIG wrapping issues with C++ --> python

Question

I'm trying to wrap a C++ file that depends on another C++ file (global.cpp) by using SWIG. I was able to get the first one to work fine, but this nested dependence seems to cause an issue. Here is my setup:

position.i

%module position
%include global.i
%{
  #include "pos.h"
%}
%include "pos.h"
%include "global.h"
... (functions declared)

position.cpp

#include <algorithm> 
#include "global.h"
#include "pos.h"
...(functions implemented)

position.h

prototypes

I then do this.

swig -c++ -python -builtin position.i
g++ -O2 -fPIC -c position.cpp
g++ -O2 -fPIC -c -I/Users/aaron/anaconda/include/python3.5m position_wrap.cxx

I have the two object files and then I bind them with

g++ -dynamiclib -lpython position.o global.o position_wrap.o -o _position.so

I've tried a number of different ways of doing this after perusing through SO and I have been totally stifled.

I get an error

 ...
 "_PyUnicode_FromFormat", referenced from:
      SwigPyObject_repr(SwigPyObject*) in position_wrap.o
      SwigPyPacked_repr(SwigPyPacked*) in position_wrap.o
      SwigPyPacked_str(SwigPyPacked*) in position_wrap.o
  "_PyUnicode_FromString", referenced from:
      _PyInit__position in position_wrap.o
      SWIG_Python_DestroyModule(_object*) in position_wrap.o
      SwigPyPacked_str(SwigPyPacked*) in position_wrap.o
  "_Py_DecRef", referenced from:
      SwigPyObject_repr(SwigPyObject*) in position_wrap.o
  "__PyObject_New", referenced from:
      _PyInit__position in position_wrap.o
...
    ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

with compilation. I've tried different linker flags by going to the path python3-config --ldflags states. I've added the -std=libstdc++ flag. I once somehow got the module to generate, but upon import to python was faced with :

ImportError:   dlopen(/Users/aaron/Desktop/swigdPython/src/_position.cpython-35m-darwin.so, 2):
    Symbol not found: __Z10e_to_ed Referenced from:
        /Users/aaron/Desktop/swigdPython/src/_position.cpython-35m-darwin.so
    Expected in: dynamic lookup"

I'm at a loss trying to figure out the proper way to link these files and was hoping someone here had some insight.

chqrlie · Accepted Answer · 2016-01-15 02:32:09Z

2

You should specify the library last on the link command line:

g++ -dynamiclib position.o global.o position_wrap.o -o _position.so -lpython

answered Jan 15, 2016 at 2:32

chqrlie

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5 Comments

Anisotropic Over a year ago

The result of this is a much smaller error message, but still receiving an undefined symbols error.

chqrlie Over a year ago

@Anisotropic: You may need to link with other libraries. Which symbols are still undefined?

Anisotropic Over a year ago

Compiler barfs out undefined "_PyInstanceMethod_New" , "_PyModule_Create2", "_PyUnicode_Concat", "_PyUnicode_FromFormat", "_PyUnicode_FromString" reference from the wrapper object. the invocation is

Thread model: posix  "/Applications/Xcode.app/Contents/Developer/Toolchains/OSX10.10.xctoolchain/usr/bin/ld" -demangle -dynamic -dylib -arch x86_64 -macosx_version_min 10.10.0 -o _sunposition.so sunpos.o global.o sunpos_wrap.o -lpython -lc++ -lSystem /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/7.0.2/lib/darwin/libclang_rt.osx.a

chqrlie Over a year ago

Do you see the libpython.dylib in the /usr/lib directory?

Anisotropic Over a year ago

Yes along with the 2.7 version of it

J.J. Hakala · Accepted Answer · 2016-01-15 02:32:16Z

2

The ordering might matter here, i.e.

g++ -dynamiclib position.o global.o position_wrap.o -lpython -o _position.so

instead of

g++ -dynamiclib -lpython position.o global.o position_wrap.o -o _position.so

answered Jan 15, 2016 at 2:32

J.J. Hakala

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Comments

Anisotropic · Accepted Answer · 2016-01-15 08:17:13Z

1

I got this to finally work using this command:

g++ -dynamiclib -o _position.so position_wrap.o position.o global.o -
I/Users/aaron/anaconda/include/python3.5m/ - L/Users/aaron/anaconda/lib/ -I/Users/aaron/Desktop/swigdPython/src -lpython3.5

I then couldn't get the module to load until exporting an environment variable:

export DYLD_LIBRARY_PATH=/Users/aaron/anaconda/lib:$DYLD_LIBRARY_PATH

answered Jan 15, 2016 at 8:17

Anisotropic

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