Mailman 3 March 2012 - Cplusplus-sig

boost::python embedding error - runtime - Mac OS X - 1.38
by Igor Karpov Oct. 1, 2014

Oct. 1, 2014

Hi, I am trying to run the following program: #include <iostream> #include <Python.h> #include <boost/python.hpp> using namespace boost::python; using namespace std; int main(int argc, char** argv) { { // Using Python/C Py_Initialize(); PyObject* main_module = PyImport_ImportModule("__main__"); PyObject* globals = PyEval_GetGlobals(); PyObject* locals = PyEval_GetLocals(); PyRun_SimpleString("print 'Hello World, from Python/C!'\n"); Py_Finalize(); } { // Using boost::python Py_Initialize(); object main_module = import("__main__"); object main_namespace = main_module.attr("__dict__"); try { object ignored = exec("print 'Hello World, from boost::python!'\n", main_namespace); Py_Finalize(); } catch (error_already_set const& e) { PyErr_Print(); return 1; } } return 0; } on Linux (both x86 and x86_64), with Ubuntu's default version of Boost (1.34.1) installed, I am able to do so as expected: $ ./embed Hello World, from Python/C! Hello World, from boost::python! on Mac OS X, I get a runtime error: $ ./embed Hello World, from Python/C! Bus Error Running with gdb, this is the stack trace: Hello World, from Python/C! Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_PROTECTION_FAILURE at address: 0x00000000 0x00000000 in ?? () (gdb) where #0 0x00000000 in ?? () #1 0x00bb618f in PyEval_GetGlobals () #2 0x00bce0dd in PyImport_Import () #3 0x00bce2b0 in PyImport_ImportModule () #4 0x008127d4 in boost::python::import (name=@0xbffff4a8) at libs/python/src/import.cpp:20 #5 0x00004446 in main (argc=1, argv=0xbffff510) at embed.cc:22 For this Mac, boost version is latest (1.38) and python version is: Python 2.5.4 (r254:67917, Dec 23 2008, 14:57:27) [GCC 4.0.1 (Apple Computer, Inc. build 5363)] on darwin Is this a bug? I attached the source and the cmake file I am using to build, for convenience. Thanks, --Igor.

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sendkeys method
by sam Sept. 30, 2013

Sept. 30, 2013

Hello, Is there away(method) in C/C++ programming that make the software think that someone pressed the OK button, similar to sendkeys in VBS (WshShell.SendKeys ("{Enter}")) Thank you, Sam

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wrapped std::vector slice affecting items in a python list
by babak April 2, 2012

April 2, 2012

Hi, I've come across some unusual behaviour that I was hoping some one might be able to explain to me. In python I have a list and a wrapped std::vector<MyCustomType> (using the vector_indexing_suite) where the list contains the items in the vector. If I slice insert items into the vector then the items in the python list change. The attached example illustrates this. Is this behaviour expected ? I'm quite confused as to what's going on so any help clarifying this would be greatly appreciated. thanks, Babak http://boost.2283326.n4.nabble.com/file/n3738972/test.py test.py http://boost.2283326.n4.nabble.com/file/n3738972/source.cpp source.cpp -- View this message in context: http://boost.2283326.n4.nabble.com/wrapped-std-vector-slice-affecting-items… Sent from the Python - c++-sig mailing list archive at Nabble.com.

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function template instantiation
by Kyle Cronan March 30, 2012

March 30, 2012

Hi all, I've been using Boost.Python to expose some instances of a class template to a python module. I ran into a problem with my class's method templates not being instantiated, leading to "undefined symbol" on import. Actually, this message from back in 2004 describes the problem exactly: http://mail.python.org/pipermail/cplusplus-sig/2004-February/006586.html The advise is to move the method definitions into the header file, but I have some methods I want to ensure are not inlined, so I ended up using explicit template instantiations instead. Kind of a pain. The standard has this to say about function template instantiations: 14.7.1 Implicit instantiation 2. Unless a function template specialization has been explicitly instantiated or explicitly specialized, the function template specialization is implicitly instantiated when the specialization is referenced in a context that requires a function definition to exist. So my question is, why isn't taking the address of some instance of a templatized function and passing it to def() enough to require the function definition to exist? Should this be considered a usability bug in the library, a problem with my compiler, or maybe neither? I'm using gcc 4.4. Thanks, Kyle Cronan

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Re : Re : Re : [boost] Re : Using an element of a class A in a constructor of a class B (reflection with boost::python)
by christophe jean-joseph March 22, 2012

March 22, 2012

Thank you for your answer, As I said, the solution I am currently using is working fine, I am just using a method explained in the tutorial for a function independant from any class: http://wiki.python.org/moin/boost.python/ExportingClasses and I extend it to a function of another class. You recommend to write things that way: class_< A_i, bp::bases<B> >(...); but, A_i are not derived from B, and as they are already derived from A_Base_j classes (some from a same base class, not all of them), I already declared their base classes. Declaring a function B::f(A& a, ...) in A as: .def("f", &B::f) keep C++ declaration (I mean, even if B::f is declared in A, it's declared as a method of B, which is correct). But what your are proposing seems not correct to me, as long as A isn't a derived class from B. Christophe Jean-Joseph ________________________________ De : Jim Bosch <talljimbo(a)gmail.com> À : christophe jean-joseph <jjchristophe(a)yahoo.fr> Envoyé le : Mercredi 21 mars 2012 4h35 Objet : Re: Re : [C++-sig] Re : [boost] Re : Using an element of a class A in a constructor of a class B (reflection with boost::python) On 03/20/2012 07:07 AM, christophe jean-joseph wrote: > > Thank you for your answer and sorry for the delay: I finally used > another solution. > I used a setParam function instead of the constructor for boost::python. > From the point of view of c++, the only difference is that the former > constructor is now just calling setParam. > This former constructor is ignored by boost::python, and instead > setParam is reflected as a normal function. > This works fine (my Python main produce, with less than 0.01% > difference, the same results as the C++ main). > But I am not satisfied with my solution for the following reason: > if A and B are 2 classes, in order to reflect a function B::f(A& a, > ....), I am writing things as follow as follow: > Class_ <A>(usual declarations here) > .def("f", &B::f) > Class_ <B>(usual declarations here) > .def("f", &B::f) > > Which means, for n classes A_i (i from 1 to n) and a function of a class > B b::f(A_1& a1, A_2& a2,...., A_n& an, ....) I'll have to write: > Class_ <A_1>(usual declarations here) > .def("f", &B::f) > . > . > . > Class_ <A_n>(usual declarations here) > .def("f", &B::f) > Class_ <B>(usual declarations here) > .def("f", &B::f) > > Which is not very clean, even though it's working. > So if there is any other way to do that, I will be glad to hear it. > I'm a little confused; if the A classes do not inherit from B, why would you want to wrap a member function of B as a method of A? I don't think they would actually work, unless you've made sure all the A classes are convertible to B by some other mechanism. And if the A classes do inherit from B, if you use: class_< A_i, bp::bases<B> >(...); with no .def("f", ...), you'll still be able to use the "f" method in Python because it will be inherited from B. Jim > ------------------------------------------------------------------------ > *De :* Jim Bosch <talljimbo(a)gmail.com> > *À :* christophe jean-joseph <jjchristophe(a)yahoo.fr>; Development of > Python/C++ integration <cplusplus-sig(a)python.org> > *Envoyé le :* Dimanche 18 mars 2012 0h22 > *Objet :* Re: [C++-sig] Re : [boost] Re : Using an element of a class A > in a constructor of a class B (reflection with boost::python) > > On 03/15/2012 09:22 AM, christophe jean-joseph wrote: > > Hello > > > > The situation is as follow. > > I have a C++ code that I haven't written and that I barely can modified. > > I am supposed to reflect this code in Python with boost. > > In the code, I have something looking like this: > > > > Class A_Base { > > A_Base(){}; > > ~A_Base(){}; > > Whatever virtual and pure virtual functions; > > } > > > > Class A_Derived{ > > A_Derived(Type1 arg1,...){whatever instructions;} > > ~A_Derived(){}; > > Whatever functions; > > } > > > > Class B { > > B(A_Base& aBase, double& x){}; > > ~B(){}; > > Whatever functions; > > } > > > > In the C++ main, at some point aDerived A_Derived is set, and then > > B(aDerived, x). > > I need to reflect that under python. > > Until now, I have been able, with a simple example, to reflect a > > function f, which is not a ctor, from a class B using A_Base& as > > argument type, but I can't figure out how to deal with it for a > constructor. > > Based on: > > > > http://wiki.python.org/moin/boost.python/ExportingClasses > > > > I am declaring f under both its class B and A_Base as follow: > > > > class_A_Base <A, boost::noncopyable>("A_Base", no_init) //this line can > > be modified > > .def("f", &B::f); > > class_B <B, boost::noncopyable>("B", init< >()) //this line can be > modified > > .def("f", &B::f); > > > > > > But when I try this for a constructor as f, it refuse to compile. > > You don't wrap constructors the same way as functions (I don't think you > can even take their address in C++). Instead, you use: > > .def(init<T1,T2,...>()) > > (where T1,T2,... are the argument types of the constructor), or do the > same thing in the init argument to class_ itself (as I've done below). > > I think what you want is something like this (assuming A_Derived does > actually inherit from A_Base, even though it doesn't in your example code): > > class_<A_Base,noncopyable>("A_Base", no_init); > class_<A_Derived,bases<A_Base>,noncopyable>("A_Derived", no_init); > class_<B,noncopyable>("B", init<A,double>()); > > Note that the float you pass in as "x" to B's constructor will not be > modified in Python; that's unavoidable in this case. > > If that doesn't work, please post exactly what you're trying to compile; > the example you posted has a few things that obviously won't compile, so > it's hard to know exactly what the problem is. > > Good luck! > > Jim > > >

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Re: [C++-sig] Managing the GIL across competing threads
by Adam Preble March 18, 2012

March 18, 2012

I edited the post so many times I forgot the subject line! I am a bad person. Maybe the most condensed question here is: How do you normally manage multiple resources competing with the GIL in a way that could cause deadlocks with it? For the details, see the long post. On Thu, Mar 15, 2012 at 11:59 PM, Adam Preble <adam.preble(a)gmail.com> wrote: > I discovered recently that during callbacks to Python objects, sometimes > the interpreter would try to do stuff at the same time, despite the fact I > made a call to ensure the GIL. I read the solution for that kind of thing > I'm doing is calling PyEval_InitThreads(). This worked at first, but like > more race conditions and stuff, all it takes is walking away from the > computer for it all to fall apart. > > What I'm seeing is a rather elaborate deadlock situation revolved around > securing the GIL. I think I need to basically put my interpreter in its > own subsystem, design-wise, and ferret calls to invoke things in the > interpreter to it, in order to ultimately get around this. However, what > I'm asking of the distribution is how they've gotten around this. > > To give something a little more concrete--this is pretty gross: > 1. Main thread starts interpreter and is running a script > 2. The script defines an implementation of callback interface A > 3. The script starts some objects that represent threads in the C++ > runtime. These are threads 1 and 2. > 4. The script starts to create an object that is wrapped from C++ > 5. The object requires a resource from thread 1, where I use promises and > futures enqueue and fulfill the request when thread #1 isn't busy. > 6. Meanwhile, the interpreter thread is waiting for the resource since it > cannot put it off any further > 7. At this point, thread 2 tries to invoke the callback to interface A, > and it needs the interpreter thread. > 8. thread #1 needs thread #2 to complete this critical step before the > get() call will complete for the master interpreter thread > 9. Thread #2 needs thread #1 to finish so it can get the GIL. It's > basically locked up in PyGILState_Ensure(). > > Heck of a deadlock. I am pondering having something else control the > interpreter in its own thread and have everybody enqueue stuff up to run in > it, like with the promises and futures I'm using elsewhere already. The > reason is that thread #2 doesn't really need to steal the interpreter at > that very exact moment. And furthermore, I'm trying to use Stackless, and > it's my understanding there I can link it up so that the interpreter gets > ahold of the Python runtime at controlled intervals--if desired--to invoke > other stuff. > > > _______________________________________________ > Cplusplus-sig mailing list > Cplusplus-sig(a)python.org > http://mail.python.org/mailman/listinfo/cplusplus-sig >

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Combining Boost Serialization with Boost Python
by James Amundson March 17, 2012

March 17, 2012

I have a use case involving Boost Serialization and Boost Python. I have a (mostly) C++ library wrapped with Python. The C++ code uses Boost Serialization to periodically create checkpoints from which the user can resume later. Getting the serialization and python libraries to work together didn't present any special problems until I had a case in which the user had a derived Python class (from a C++ base). In searching the web, I have seen people asking about similar cases, but never an answer. See, e.g., http://stackoverflow.com/questions/7289897/boost-serialization-and-boost-py… <http://stackoverflow.com/questions/7289897/boost-serialization-and-boost-py…> . I have a partial solution to the problem using Boost Serialization and Python Pickle together. I would appreciate any advice on how to improve it. My solution is limited in that the state of the base C++ object is not restored. I also get an extra copy of the C++ object. Since my current use case has no state in the base object, I can live with these limitations. I would however, like to find a full solution. In the files I have attached, I can successfully run three variations on a simple test case. A class of type Base is passed to a class of type Caller. Caller calls the passed class's doit method twice, saves (checkpoints) its state, then calls the doit method again. The resume script restores the state of the Caller and Base classes, then calls the doit method again. If successful, the resumed doit call should be the same as the third doit call from the original script. In testcheckpoint1.py, the Base class is the original (C++) Base. It has no state, so the example is pretty trivial. Its doit method prints "Base::doit" -------------------------------------------------------------------------- % python testcheckpoint1.py Base::doit Base::doit checkpointed here Base::doit % python testresume.py resuming... Base::doit -------------------------------------------------------------------------- In testcheckpoint2.py I pass a derived Python class to Caller. The derived doit method displays "Derived:doit" and a counter: -------------------------------------------------------------------------- % python testcheckpoint2.py Derived::doit count = 1 Derived::doit count = 2 checkpointed here Derived::doit count = 3 % python testresume.py resuming... Derived::doit count = 3 -------------------------------------------------------------------------- In testcheckpoint3,py, I use a derived Python class with a non-trivial constructor, which is used to set the initial value of the counter: -------------------------------------------------------------------------- % python testcheckpoint3.py Derived2::doit count = 5 Derived2::doit count = 6 checkpointed here Derived2::doit count = 7 % python testresume.py resuming... Derived2::doit count = 7 -------------------------------------------------------------------------- As you can see, many things are possible with the code the way it currently exists. I would still like to figure out how to preserve the state of the base class. Any and all advice will be appreciated. --Jim Amundson <http://stackoverflow.com/questions/7289897/boost-serialization-and-boost-py…>

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Re : [boost] Re : Using an element of a class A in a constructor of a class B (reflection with boost::python)
by christophe jean-joseph March 17, 2012

March 17, 2012

Hello The situation is as follow. I have a C++ code that I haven't written and that I barely can modified. I am supposed to reflect this code in Python with boost. In the code, I have something looking like this: Class A_Base { A_Base(){}; ~A_Base(){}; Whatever virtual and pure virtual functions; } Class A_Derived{ A_Derived(Type1 arg1,...){whatever instructions;} ~A_Derived(){}; Whatever functions; } Class B { B(A_Base& aBase, double& x){}; ~B(){}; Whatever functions; } In the C++ main, at some point aDerived A_Derived is set, and then B(aDerived, x). I need to reflect that under python. Until now, I have been able, with a simple example, to reflect a function f, which is not a ctor, from a class B using A_Base& as argument type, but I can't figure out how to deal with it for a constructor. Based on: http://wiki.python.org/moin/boost.python/ExportingClasses I am declaring f under both its class B and A_Base as follow: class_A_Base <A, boost::noncopyable>("A_Base", no_init) //this line can be modified .def("f", &B::f); class_B <B, boost::noncopyable>("B", init< >()) //this line can be modified .def("f", &B::f); But when I try this for a constructor as f, it refuse to compile. Anyone got a clue? Thank you very much in advance for any further help.

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(no subject)
by Adam Preble March 16, 2012

March 16, 2012

I discovered recently that during callbacks to Python objects, sometimes the interpreter would try to do stuff at the same time, despite the fact I made a call to ensure the GIL. I read the solution for that kind of thing I'm doing is calling PyEval_InitThreads(). This worked at first, but like more race conditions and stuff, all it takes is walking away from the computer for it all to fall apart. What I'm seeing is a rather elaborate deadlock situation revolved around securing the GIL. I think I need to basically put my interpreter in its own subsystem, design-wise, and ferret calls to invoke things in the interpreter to it, in order to ultimately get around this. However, what I'm asking of the distribution is how they've gotten around this. To give something a little more concrete--this is pretty gross: 1. Main thread starts interpreter and is running a script 2. The script defines an implementation of callback interface A 3. The script starts some objects that represent threads in the C++ runtime. These are threads 1 and 2. 4. The script starts to create an object that is wrapped from C++ 5. The object requires a resource from thread 1, where I use promises and futures enqueue and fulfill the request when thread #1 isn't busy. 6. Meanwhile, the interpreter thread is waiting for the resource since it cannot put it off any further 7. At this point, thread 2 tries to invoke the callback to interface A, and it needs the interpreter thread. 8. thread #1 needs thread #2 to complete this critical step before the get() call will complete for the master interpreter thread 9. Thread #2 needs thread #1 to finish so it can get the GIL. It's basically locked up in PyGILState_Ensure(). Heck of a deadlock. I am pondering having something else control the interpreter in its own thread and have everybody enqueue stuff up to run in it, like with the promises and futures I'm using elsewhere already. The reason is that thread #2 doesn't really need to steal the interpreter at that very exact moment. And furthermore, I'm trying to use Stackless, and it's my understanding there I can link it up so that the interpreter gets ahold of the Python runtime at controlled intervals--if desired--to invoke other stuff.

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multiple modules per dll/so?
by Michael Schuitema March 14, 2012

March 14, 2012

I would like to create a python package with several submodules, eg parent parent.child1 parent.child2 A number of the submodules use C++ extension made available via boost.python. Do I need to create a separate dll for each of them or is there a way to expose several packages with one dll? Can I have BOOST_PYTHON_MODULE(child1) BOOST_PYTHON_MODULE(child2) etc in a single dll. Cheers, mike

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