Mailman 3 October 2015 - Cplusplus-sig

PyUblas: PROBLEMS WITH PythonBoost libraries
by Gabriele Brambilla Oct. 21, 2015

Oct. 21, 2015

Hi all, I tried to install PyUblas via pip install but I received an error about the Boost python libraries. I have a Mac and I am using Anaconda for Python I tried manually doing: 1 11:31 setenv CPPFLAGS "-I/opt/local/include" 2 11:31 setenv LDFLAGS "-L/opt/local/lib" 3 11:31 cd /tmp 4 11:31 tar zxf ~/Downloads/PyUblas-2013.1.tar.gz 5 11:31 cd PyUblas-2013.1/ 6 11:32 ./configure.py 7 11:32 vi siteconf.py The siteconf.py edit was changing BOOST_PYTHON_LIBNAME = ['boost_python'] to BOOST_PYTHON_LIBNAME = ['boost_python-mt'] 8 11:32 python setup.py install the install complete, but when I try to import pyublas I got this error: but "import pyublas" fails with: [gs66-stumbras:~] gbrambil% python Python 2.7.6 (default, Dec 12 2014, 14:02:59) [GCC 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import pyublas Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/Users/gbrambil/anaconda/lib/python2.7/site-packages/PyUblas-2013.1-py2.7-macosx-10.5-x86_64.egg/pyublas/__init__.py", line 2, in <module> import pyublas._internal ImportError: dlopen(/Users/gbrambil/anaconda/lib/python2.7/site-packages/PyUblas-2013.1-py2.7-macosx-10.5-x86_64.egg/pyublas/_internal.so, 2): Symbol not found: __ZNSoD0Ev Referenced from: /Users/gbrambil/anaconda/lib/python2.7/site-packages/PyUblas-2013.1-py2.7-macosx-10.5-x86_64.egg/pyublas/_internal.so Expected in: dynamic lookup >>> Confirming missing symbol: [gs66-stumbras:~] gbrambil% nm /Users/gbrambil/anaconda/lib/python2.7/site-packages/PyUblas-2013.1-py2.7-macosx-10.5-x86_64.egg/pyublas/_internal.so | grep __ZNSoD0Ev U __ZNSoD0Ev Do you know what the problem is? Thanks Gabriele

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pybind11 -- alternative to Boost.Python
by Wenzel Jakob Oct. 20, 2015

Oct. 20, 2015

Hello all, after being a long-time Boost.Python user, I’ve been working on an alternative that makes more effective use of recent C++11-capable compilers. The overall syntax and ideology are very similar to Boost.Python, but the implementation only requires a few header files with a a vastly smaller amount of code thanks to C++11 lambda functions, tuples and variadic templates. There is also dedicated support for Python’s buffer protocol and NumPy arrays, which is useful for scientific computing applications. So far it’s only used by a few projects, but I think it could be useful to this audience. Code: https://github.com/wjakob/pybind11 <https://github.com/wjakob/pybind11> Documentation: http://pybind11.readthedocs.org/en/latest/ <http://pybind11.readthedocs.org/en/latest/> Best, Wenzel

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Returning C++ buffer to Python 2.7
by Tony Cappellini Oct. 19, 2015

Oct. 19, 2015

I've allocated memory in C++ and need to expose a function to Python so that Python can read this memory as a sequence. I've found this example http://pastebin.com/YGi61R4H from this URL http://stackoverflow.com/questions/16232520/how-to-expose-raw-byte-buffers-… which **looks** like it will do what I need, from the description of the code and the request from the original author. However, it looks incomplete to me. There is no code which defines, or explains what *handle<>* is/does, in this line of code object retval = object(handle<>(py_buf)); I would appreciate some help trying to accomplish this (my statement in the first line of this message). Useful (working) examples of Boost-to-Python code are not easily found outside of Stackoverflow. Thanks Tony

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Boost.Python: C++ object in python: Cannot add to C++ base class list.
by Christoff Kok Oct. 9, 2015

Oct. 9, 2015

Hi, I am trying to extend existing C++ objects in Python via inheritance. I can do this successfully and run virtual methods overridden in Python. When I however, try to add the python object to a list of pointers of the C++ Base object type(the Base object the python class has overridden), I get a type error: 'Attempting to append an invalid type' I am sure this error is due to there begin no 'implicitly_convertible' functionality from derived* to base*. In C++, this would be defined as so: implicitly_convertible<[Derived_from_base]*,Base*>();. Is it possible to define this in python? How can I achieve this? Here is sample code reproducing this behaviour. *C++* struct Base { virtual ~Base() {} virtual int f() = 0; }; struct A { std::vector<Base*>& GetBaseList() { return m_base_List; } std::vector<Base*> m_base_List; }; struct BaseWrap : Base, wrapper<Base> { int f() { return this->get_override("f")(); } }; BOOST_PYTHON_MODULE(sandbox) { class_<BaseWrap, Base*, boost::noncopyable>("Base", no_init) .def("f", pure_virtual(&Base::f)); class_<A, A*>("A", init<>()) .add_property("baseList", make_function(&A::GetBaseList, return_internal_reference<>())); //implicitly_convertible<[Derived_from_base]*,Base*>(); class_<std::vector<Base*>>("BaseList").def(vector_indexing_suite<std::vector<Base*>>()); } *Python* from sandbox import * class derived(Base): def __init__(self): self.name = "test" def f(self): print("Hello Derived!") d = derived() d.f() # Output: Hello Derived! a = A() a.baseList.append(d) # TypeError: Attempting to append an invalid type Any help or ideas will be greatly appreciated. Regards, Christoff

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Boost.Python: Set pointer error.
by Christoff Kok Oct. 5, 2015

Oct. 5, 2015

Hi, I am trying to set a raw pointer variable in a wrapped C++ class through python and I receive the following error: Boost.Python.ArgumentError: Python argument types in None.None(A, P) did not match C++ signature: None(AWrapper {lvalue}, P {lvalue}) This is the C++ code: #include <boost/python.hpp> #include <boost/python/suite/indexing/vector_indexing_suite.hpp> #include <vector> using namespace boost::python; class P { private: int m_amount = 3; public: int GetAmount() { return m_amount; } void SetAmount(int val) { m_amount = val; } }; class A { public: P* GetP() { return m_p;} void SetP(P* val) { m_p = val;} private: P* m_p; }; class Cont { public: P* createP() {auto p = new P(); m_pList.push_back(p); return p;} std::vector<P*>& GetPList() { return m_pList; } private: std::vector<P*> m_pList; }; struct AWrapper : A, wrapper<A> { void wrapper_SetP(P& p) {this->SetP(&p);} }; BOOST_PYTHON_MODULE(sandbox) { class_<AWrapper, A*>("A", init<>()) .add_property("p", make_function(&A::GetP, return_internal_reference<>()), &AWrapper::wrapper_SetP); class_<Cont>("Cont", init<>()) .def("createP", make_function(&Cont::createP, return_internal_reference<>())) .add_property("pList", make_function(&Cont::GetPList, return_internal_reference<>())); class_<P, P*>("P", init<>()) .add_property("amount", &P::GetAmount, &P::SetAmount); class_<std::vector<P*>>("PList").def(vector_indexing_suite<std::vector<P*>>()); } This is the Python code: import sandbox cont = sandbox.Cont() p1 = cont.createP() print(cont.pList[0].amount) a = sandbox.A() a.p = p1 Any help will be greatly appreciated. I've been struggling with this for a while now. Regards, -- Christoff Kok Software Engineer Ex Mente http://www.ex-mente.co.za christoff.kok(a)ex-mente.co.za PO Box 10214 Centurion 0046 South Africa tel: +27 12 743 6993 tel: +27 12 654 8198 fax: +27 85 150 1341

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