Mailman 3 August 2006 - Cplusplus-sig

Working with python unicode strings without wstring
by Rod Cloutier Aug. 6, 2006

Aug. 6, 2006

Hi, I am trying to wrap an external library that uses "const wchar_t *" a arguments for several methods. I know that if they would have used std::wstring the conversion would have been straight forward. Is there anyway to convert python unicode string to wchar_t pointers ? Can I make the following code work without writting a wrapper function that uses a wstring as an argument ? in C++: void printText( const wchar_t* str ) { std::wcout << str; } in python: MyModule.printText( u"The message" ) Thanks Rodrigue Cloutier

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Overriding operator= in boost python
by Will Lee Aug. 4, 2006

Aug. 4, 2006

Hi, Is there any way to wrap the operator= for a C++ assignment operator in boost python? The documentation on operators doesn't seem to allow that ( http://www.boost.org/libs/python/doc/v2/operators.html). Essentially, I would like to do the python equalivalent of: class A; class B : public A; I then have: B& operator=(const A& a) { // assign A to B } So that I can do (say bHolder is a class that contains a B instance): a = A(); bHolder.b = a; Thanks, Will

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Pyplusplus: Exporting arrays of non-copyable type?
by Haridev, Meghana Aug. 4, 2006

Aug. 4, 2006

Hi Folks, I'm using pyplusplus to generate boost.python wrappers for the following piece of C++ code: ------------------------------------------------------------------------ ----------- //test.cpp class Base { protected: Base() { } private: // Copy constructor and assignment operator should not // be used. Base(const Base&); const Base& operator=(const Base&); }; class Derv: public Base { public: int x; }; class Test: public Base { public: Derv dataArray[20]; }; ------------------------------------------------------------------------ ------------- In class Test, the dataArray if of type Derv which is a non-copyable type (because of private copy constructor and assignment operator of Base class). In other words, this is not allowed: >> obj = Test() >> obj.dataArray[0] = Derv() #Not allowed But the pyplusplus generated code (register_array_1() in __array_1.pypp.hpp) exposes a set_item method for the data array though it's type is non-copyable and hence the code does not compile with the following error message: ------------------------------------------------------------------------ ------------- test.cpp:8: error: 'const Base& Base::operator=(const Base&)' is private test.cpp:11: error: within this context __array_1.pypp.hpp: In member function 'void pyplusplus::containers::static_sized::array_1_t<TItemType, size>::set_item(long unsigned int, typename boost::call_traits<const TItemType>::param_type) [with TItemType = Derv, long unsigned int size = 20ul]': __array_1.pypp.hpp:73: warning: synthesized method 'Derv& Derv::operator=(const Derv&)' first required here ------------------------------------------------------------------------ ------------- Please see attached source/generated files. Is there any way I can make pyplusplus to NOT generate the set_item method for arrays of non-copyable type? (maybe by setting some flag?) Thanks, -Meghana.

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Converter with return_value_policy<manage_new_object> semantics...
by Kevin Jones Aug. 3, 2006

Aug. 3, 2006

Hi all, I have a function T foo(). The problem is that T is a variant type and by default is being converted to a python object using my supplied converter. I would like to rewrite the converter to use return_value_policy<manage_new_object> semantics on a case by case basis for each variant type. Any suggestions? Best regards, Kevin __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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[Boost.Python] Using bbv2 to build simple extension
by Roberto Aguilar Aug. 3, 2006

Aug. 3, 2006

Hello, I'm trying to setup my build environment to properly build a python extension outside of the boost tree using Boost.Build v2. So far I have this tree setup: top/ | +-- Jamroot | +-- lib/ | | | +-- pytest | | | `-- Jamfile | `-- python.cpp My Jamroot file looks like: ---- .boost-root = /Users/berto/apps/opt/boost_1_33_1 ; use-project /boost : $(.boost-root) ; using python : 2.4 : /sw ; project myproj : requirements <link>static ; ---- My Jamfile: ---- project : usage-requirements <include>. ; [...] python-extension fileformats_py : python.cpp : <library>/boost/python//boost_python ; ---- In the jamfile I also have some library declarations, but they're irrelevant to this. When I run bjam, I get this: [berto@drjekyll][1108]$ bjam Building Boost.Regex with the optional Unicode/ICU support disabled. Please refer to the Boost.Regex documentation for more information (and if you don't know what ICU is then you probably don't need it). error: Unable to find file or target named error: '/python//python_for_extensions error: referred from project aterror: '.' My guess is that I'm missing some sort of declaration in my Jamroot file. Any help is much appreciated! Thanks! -Roberto.

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[boost.python] conversion between string and unsigned char *
by Jan Langer Aug. 3, 2006

Aug. 3, 2006

Hello, I have a library I want to expose to python by using boost.python and pyplusplus. This library works completely with unsigned char * for strings. My current approach is // library typedef unsigned char * StringT; StringT F_ApiGetString (F_ObjHandleT docId, F_ObjHandleT objId, IntT propNum); // boost.python code struct StringT_converter { static PyObject *convert (StringT s) { return bp::incref (bp::str (reinterpret_cast <char *> (s)).ptr ()); } }; BOOST_PYTHON_MODULE(pyfdk){ bp::to_python_converter <StringT, StringT_converter> (); bp::def("F_ApiGetString" , &::F_ApiGetString , ( bp::arg("arg0"), bp::arg("arg1"), bp::arg("arg2") ) , bp::return_value_policy< bp::return_by_value, bp::default_call_policies >() ); } But somehow it does not work: TypeError: No to_python (by-value) converter found for C++ type: char Actually, I must free the memory of the returned StringT, but I am not sure if I can savely change the converter like this: struct StringT_converter { static PyObject *convert (StringT s) { PyObject *p = bp::incref (bp::str (reinterpret_cast <char *> (s)).ptr ()); F_ApiDeallocate(s); return p; } }; I hope someone can help me. Thanks, Jan

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Pyplusplus - anonymous union
by Jan Langer Aug. 2, 2006

Aug. 2, 2006

Hello, I'm using pyplusplus to generate python-bindings for a C API. However, there are several unions, and I just don't know how to handle them. The following example code from the API: typedef struct { int offset; int dataType; union { char *sdata; int idata; } u; } A; generates this Boost.Python code: bp::class_< A >( "A" ) .def_readwrite( "offset", &A::offset ) .def_readwrite( "dataType", &A::dataType ) .def_readonly( "u", &A::u ); and it does not compile on gcc 3.3.2 with this error: error: template-argument `A::<anonymous union> A::*' uses anonymous type Is there a solution? I have already searched the news archives, but haven't found useful hints. Thanks, Jan

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wrapping abstract bases whose virtual functions should *not* be overridden in Python
by Mark Kirk Aug. 2, 2006

Aug. 2, 2006

Hi... I'm using using boost::python for the first time to wrap a C++ lib. I'm extremely impressed with it, and I offer a warm thank-you to Dave and others on the boost::python team for creating it. I've been working with it for a couple of days, and I've read the tutorial and other bits of the Boost docs; I think most of it has sunk in. However, I'm having trouble with something: I have an abstract base class (one+ pure virtuals). I do *not* want any of these virtual functions overridden from within Python; I'm quite happy with the implementations in the C++ derived classes. This is an in-house lib, and the C++ implementation is and should remain the canonical implementation. In the docs, there are a couple of sections which address abstract bases ("Class Virtual Functions" subsection in the tutorial and the wrapper.hpp docs). Both state the procedure outlined is for wrapping bases for which you wish the ability to override the virtuals from *within* Python. Again, I explicitly do *not* want this ability. So, how do I correctly wrap my abstract base? I get errors complaining about the the virtual functions being abstract. Must I still use the wrapper<> procedure in my situation? If so, how do I prevent overriding of my virtuals in Python? Or, is there another way entirely? Thanks for your help, and let me know if you need clarification. mark

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Boost.Python shared_ptr container gotchas
by John Reid Aug. 1, 2006

Aug. 1, 2006

Hi, I use boost::shared_ptr to manage lifetimes of objects. I've run into a couple of problems using these inside containers with Boost.Python. I thought I could share my experiences and perhaps get some useful feedback or help others avoid these problems. 1) Exposing a vector< shared_ptr< T > > through the indexing suite was giving me headaches. I couldn't work out why I couldn't access the elements from python. I kept getting a runtime error about no python class for boost::shared_ptr< T > even after I was registering the pointer type. It turns out that my problem was the vector indexing suite was trying to wrap a reference to the boost::shared_ptr< T > in a python object. I needed to set the NoProxy template parameter on vector_indexing_suite to true and that solved all those issues. Once I understood what was happening the answer was clear. Until that moment there was a lot of head-scratching. The documentation is factually comprehensive but I wonder whether it couldn't have more use cases that explain why certain things are necessary. 2) This was a slightly more insidious problem. I also use the shared_ptrs as keys in associative containers. I ensure that equal objects are always identical (i.e. share the same address) so that I can just compare addresses rather than contents. The trouble was that operator< for shared_ptrs seemed to be comparing more than just the address of the pointee. If a shared_ptr made a round trip through python and back again it would not be equal (not greater nor less than) to the original shared_ptr under the operator< relationship. I fixed this by changing the ordering on my map to: struct smart_ptr_less_than { template< typename T > bool operator()( T p1, T p2 ) const { return p1.get() < p2.get(); } }; AFAIK this is defines a valid weak ordering. I'm not sure why operator< on shared_ptrs is not defined like this. Something to do with the deleter stored for shared_ptrs perhaps? I hope this proves useful to someone or that I can be corrected and learn something in the process. Regards, John.

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Pyplusplus: Removing generation of bp::implicitly_convertible code?
by Haridev, Meghana Aug. 1, 2006

Aug. 1, 2006

I'm using pyplusplus to generate boost.python wrappers for the following piece of code: //test.h class Y { }; class X { public: X(const Y *yptr = 0){ } }; Pyplusplus generates the corresponding boost.python code for it: // This file has been generated by pyplusplus. #include "boost/python.hpp" #include "test.h" namespace bp = boost::python; BOOST_PYTHON_MODULE(TEST){ bp::class_< Y >( "Y" ); bp::class_< X >( "X", bp::init< bp::optional< Y const * > >(( bp::arg("yptr")=bp::object() )) ); bp::implicitly_convertible< Y const *, X >(); } Two Questions: ---------------------- Question 1: How can I make pyplusplus to NOT generate the implicitly convertible boost code? I do not want to take advantage of the conversion facility. Basically, I want the pyplusplus generated code to look like this: BOOST_PYTHON_MODULE(TEST){ bp::class_< Y >( "Y" ); bp::class_< X >( "X", bp::init< bp::optional< Y const * > >(( bp::arg("yptr")=bp::object() )) ); //bp::implicitly_convertible< Y const *, X >(); - Do not want to generate } ----- OR ------ Question 2: Is there any way I can expose only the default no-arg constructor for class X i.e X( ) and not expose the constructor X(const Y *yptr = 0)? That is, expose class X as: bp::class_< X >( "X", bp::init< >( ) ). That would automatically take care of not generating the bp::implicitly_convertible code also. Generated code should look like this: BOOST_PYTHON_MODULE(TEST){ bp::class_< Y >( "Y" ); bp::class_< X >( "X", bp::init< >( ) ); //Expose just default constructor //bp::implicitly_convertible< Y const *, X >(); - Will not be generated } I also tried excluding constructors for class X, but it excludes all the constructors. I want to be able to select and just exclude the X(const Y *yptr = 0) constructor. Is it possible to selectively exclude constructors from being exposed to C++ using pyplusplus? Thanks, -Meghana.

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