Import Error on boost python hello program

Question

include

using namespace boost::python;

struct World{
    void set(std::string msg) { this->msg = msg; }
    std::string greet() { return msg; }
    std::string msg;
};

BOOST_PYTHON_MODULE(hello)
{
    class_<World>("World")
        .def("greet", &World::greet)
        .def("set", &World::set)
    ;
}

Compile and build ok

~/boost$ g++ -fPIC -I/usr/include/python2.6 -c hello.cpp 
~/boost$ g++ -shared hello.o -o hello.so

But when import from python side, got error.

>>> import hello.so
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: ./hello.so: undefined symbol: _ZNK5boost6python7objects21py_function_impl_base9max_arityEv
>>>

Community · Accepted Answer · 2017-05-23 11:54:56Z

14

Solved this via "No such file or directory" error with Boost Python

g++ -c -fPIC hello.cpp -o hello.o
g++ -shared -Wl,-soname,hello.so -o hello.so  hello.o -lpython2.6 -lboost_python

did the trick for me. I hope this is as clear as possible as i was struggling with this for about half an hour now ;)

edited May 23, 2017 at 11:54

CommunityBot

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answered Aug 19, 2010 at 18:12

user118861

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Comments

Yu Huang · Accepted Answer · 2013-08-30 18:26:22Z

7

same as other post here

g++ -c -fPIC hello.cpp -o hello.o
g++ -shared -Wl,-soname,hello.so -o hello.so  hello.o -lpython2.6 -lboost_python

But i want to stress the importance of the position of "-lpython2.6 -lboost_python". If you put them in front of input files (hello.o), they will be somehow ignored (not linked to the final hello.so). This is at least true for g++ (Ubuntu/Linaro 4.6.3-1ubuntu5).

To be simple, http://ubuntuforums.org/showthread.php?t=496287 suggested:

  g++ <.cpp or .o file(s)> [LDFLAGS] [LIBS] -o [appname]

edited Aug 30, 2013 at 18:26

answered Aug 16, 2013 at 18:14

Yu Huang

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1 Comment

Emmet Over a year ago

As I understand it, the reason for the link-order sensitivity is that the GNU ld compile-time linker is a one-pass linker: it picks up symbols to resolve from left-to-right on the command-line, and maintains a list of unresolved symbols, so if hello.o is at the end, it introduces new unresolved symbols (that are defined in libpython2.6.so and libboost_python.so), but they can't now be resolved because there's nothing to the right that defines those symbols.

Community · Accepted Answer · 2017-05-23 11:47:01Z

4

Oh, I just saw this post:

help needed with boost python

and problem solved

edited May 23, 2017 at 11:47

CommunityBot

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answered Nov 22, 2009 at 21:12

user216056

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2 Comments

Christopher Bruns Over a year ago

So was the solution to add "-lpython2.6 -lboost_python" to the link line? It is not completely clear to me what you learned from the other thread...

Tijme Over a year ago

@ChristopherBruns Did you ever get a solution for this?

Jakobovski · Accepted Answer · 2016-11-20 15:25:51Z

3

I had the same issue and it turned out that I was missing a constructor on my class.

answered Nov 20, 2016 at 15:25

Jakobovski

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1 Comment

John C Over a year ago

Just had the same error, this one was so bloody sneaky!! Thanks a bunch for this remark, it could have taken me days until I noticed this

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