Mailman 3 June 2005 - Cplusplus-sig

wrapping a to_python_converter
by Andreas Beyer June 24, 2005

June 24, 2005

Assume I have a class A and a shared pointer to it A_ptr. BP converts A_ptr correctly to python after regestring the pointer: BOOST_PYTHON_MODULE(ptr_test) { ... python::register_ptr_to_python< A::A_ptr >(); ... } Now, I want to call a function f() each time a pointer of type A_ptr is returned to python. The function f() does not modify A, nor does it change the way A's should be converted to python. In fact, f() only registers the pointer (see below). I guess I would somehow have to wrap the existing converter. Is that the correct idea? But "where" is this converter? (Thus, how/where does the register_ptr_to_python template create and register the actual converter?) Does anybody have an example of such wrapped to_python_converter? The questions may sound a bit stupid, but I never have done anything low-level with BP. Specifically I never wrote a to_python_converter. In the concrete example I want to call this function before returning A_ptr: template <class T> void hold_python(shared_ptr<T>& x) { x = python::extract<shared_ptr<T> >( python::object(x) ); } Here python::object(x) will call the to_python_converter. Thus, if hold_python() would be called from within a to_python_converter I would have to avoid recursion, right? I guess hold_python() must explicitely call the standard to_python_converter. How do I do that? Thanks!! Andreas

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boost on OS X
by Gary Robinson June 23, 2005

June 23, 2005

Hi, I'm a beginner with respect to boost. And I'm not too experienced with Unix either, so my questions are newbie ones. I'm trying to get it to install on OS X 10.3.9. After reading various discussions on installing boost on OS X that I could find online, I tried this: bjam "-sPYTHON_ROOT=/System/Library/Frameworks/Python.framework" "-sPYTHON_VERSION=2.3" "-sTOOLS=darwin" "-sRUN_ALL_TESTS=1" "test" I got the response: ...found 2 targets... And no other response. I expected to find output results in /usr/local, but found nothing there. Any help would be most appreciated! Thanks, Gary -- Gary Robinson Emergent Music, LLC grobinson(a)goombah.com Company: http://www.goombah.com Blog: http://www.garyrobinson.net

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Passing messages from C++ to python
by Ram, Siddharth June 23, 2005

June 23, 2005

I have a bunch of C++ code that has sucessfully been exported to python. I have a question about how I could use boost to send messages from C++ to Python. The setup is somewhat complex, please bear with me Here is my setup: 1 or more C++ (p)threads are executing I have started the python interpreter in another pthread I import the .so created via boost into the interpreter (which is attached to /dev/tty) So now, I can call methods in the C++ threads from the python interpreter. All commands exported to commands result in messages being posted on a queue. It gets picked up by the C++ thread and consumed. Now, I would like to be able to do this from the C++ thread to Python. Imagine that some timer expires in the C++ thread and it wants to send a message to a listener in python. I have created another pthread which gets signaled via a condition variable, recieves the message, and does a PyRun_SimpleString (after grabbing the global interpreter lock and all that good stuff). My question is this: How do I pass parameters from C++ to Python receive thread ? They use the same types which I have exported to python via Boost, but Py_BuildValue does not have a way of saying '..take this C++ object and create this corresponding PyObject which you already know about'. The only way I can think of doing this is by writing a conversion function, which I am trying to avoid. And I should not really need to do this, since Python already knows the type. Can Boost help with this? Thanks for any help. BTW, If it is not obvious, I am a newcomer to Boost.Python. It really rocks. Thanks to David and others for an awesome tool.

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Re: [C++-sig] Passing messages from C++ to python
by Petrucio June 23, 2005

June 23, 2005

I did not took the time to fully read your question and setup, so forgive me if my answer is not what you need. But to pass parameters or call code from C++ to Python, the easiest way to do this is to implement a polymorphic function in C++ to receive these, and reimplement that in Python. Something like this: class CppReceiver { public: virtual void receiveParameters(SomeClass parm1, ...) {} } Export this class and reimplement that in Python, doing whatever you want in it: def class PythonReceiver: def receiveParameters(parm1, ...): ... Now all you have to do is create an instance of that extended python class and pass it to the c++ code that will do the calling. When any C++ code calls the receiveParameters of your python create instance, the python code you implemented will be called. Petrucio At 15:46 23/6/2005, you wrote: >I have a bunch of C++ code that has sucessfully been exported to >python. I have a question about how I could use boost to send messages >from C++ to Python. The setup is somewhat complex, please bear with me > >Here is my setup: > >1 or more C++ (p)threads are executing > >I have started the python interpreter in another pthread > >I import the .so created via boost into the interpreter (which is >attached to /dev/tty) > >So now, I can call methods in the C++ threads from the python >interpreter. All commands exported to commands result in messages being >posted on a queue. It gets picked up by the C++ thread and consumed. > > >Now, I would like to be able to do this from the C++ thread to Python. >Imagine that some timer expires in the C++ thread and it wants to send a >message to a listener in python. I have created another pthread which >gets signaled via a condition variable, recieves the message, and does a >PyRun_SimpleString (after grabbing the global interpreter lock and all >that good stuff). > >My question is this: How do I pass parameters from C++ to Python receive >thread ? They use the same types which I have exported to python via >Boost, but Py_BuildValue does not have a way of saying '..take this C++ >object and create this corresponding PyObject which you already know >about'. The only way I can think of doing this is by writing a >conversion function, which I am trying to avoid. And I should not really >need to do this, since Python already knows the type. Can Boost help >with this? > >Thanks for any help. BTW, If it is not obvious, I am a newcomer to >Boost.Python. It really rocks. Thanks to David and others for an awesome >tool. >_______________________________________________ >C++-sig mailing list >C++-sig(a)python.org >http://mail.python.org/mailman/listinfo/c++-sig

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ANN: Boost.Python bindings for OpenGL
by Ralf W. Grosse-Kunstleve June 23, 2005

June 23, 2005

The GL Toolbox (gltbx) provides Python bindings for OpenGL GL_* and GLU_* defines, and gl*() and glu*() functions. The original C interfaces are preserved as much as possible. Except for the functions that may appear between calls of glBegin() and glEnd(), OpenGL errors are converted to Python exceptions. All functions support Python keyword arguments. For more information visit: http://cci.lbl.gov/gltbx/ __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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Question about Boost.Python and unsigneds
by Ram, Siddharth June 23, 2005

June 23, 2005

I have the following in my Boost Module: #include <boost/python.hpp> using namespace boost::python; #include "RLPTypesPkg.h" BOOST_PYTHON_MODULE (RLPTypesPkg) { def("RLPDEFS_CONFIG_INITIAL",RLPDEFS_CONFIG_INITIAL); [...] Where RLPDEFS_CONFIG_INITIAL is defined to be an unsigned int. When I build this, I get the following error. I was under the impression (from the tutorial) that unsigneds are mapped to Python longs ? Any help would be appreciated -Siddharth /usr/include/boost/python/make_function.hpp: In function `boost::python::api::object boost::python::make_function(F) [with F = unsigned int]': /usr/include/boost/python/def.hpp:82: instantiated from `boost::python::api::object boost::python::detail::make_function1(T, ...) [with T = unsigned int]' /usr/include/boost/python/def.hpp:91: instantiated from `void boost::python::def(const char*, Fn) [with Fn = unsigned int]' test/boost_rlp/boost_RLPTypesPkg.cpp:6: instantiated from here /usr/include/boost/python/make_function.hpp:103: error: no matching function for call to `get_signature(unsigned int&)'

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boost::python & precomp headers problem
by Ira June 23, 2005

June 23, 2005

Hi, I'm new to boost so don't assume I've tried *anything* to solve this (though I assure you I have). First off, I'm Using VC6. When trying to '#include <boost/python.hpp>' in cpp files it works fine. When trying that include in the precompiled headers, I get the following d:\visual studio projects\boost_1_32_0\boost\ref.hpp(50) : fatal error C1001: INTERNAL COMPILER ERROR (compiler file 'msc1.cpp', line 1786) Please choose the Technical Support command on the Visual C++ Help menu, or open the Technical Support help file for more information Any way around this? If this is the wrong group for this post, please let me know. Thanks, Ira

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BPL and Py_Clear()
by Niall Douglas June 21, 2005

June 21, 2005

How well does BPL handle Py_Clear() being called on a wrapped object instance when there are still plenty of referants around? What happens if something tries to access the wrapped object instance after it has been cleared? Does it get None, or does it crash? Cheers, Niall

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Python string -> const char * + size_t
by Eric Hopper June 21, 2005

June 21, 2005

I'm trying to connect a hash function written in C++ to Python. This function will be processing a ton of data. In Python, it's quite natural to store random data in a string. It's my impression that when boost::python converts that string to a ::std::string it makes a copy of it. For this application, that will add a significant amount of CPU to the time for processing the data, and that's important. I would like instead to pass in pointers that point into the internal data structure that Python is storing the string in. The hash function is only going to read it and munge it a bit, so as long as the data remains around for the duration of the call, it's not a problem. I want to somehow pass a Python string to an interface something like: class Something { public: void hash_data(const char *data, size_t datalen); }; What is the easiest and cleanest way to make this happen using boost::python? I'm willing to write a wrapper that has a slightly different (and possibly boost::python specific) interface as long as the wrapper sucks up very little CPU time. I do want to manipulate Something objects in other ways in the Python interpreter. Thanks, -- "It does me no injury for my neighbor to say there are twenty gods or no God. It neither picks my pocket nor breaks my leg." --- Thomas Jefferson "Go to Heaven for the climate, Hell for the company." -- Mark Twain -- Eric Hopper (hopper(a)omnifarious.org http://www.omnifarious.org/~hopper) --

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pyste cache
by Scott McKay June 20, 2005

June 20, 2005

I've noticed that the pyste cache doesn't detect changes like a declared method in a header having a default implementation added there, resulting in the changes being ignored. Would it be useful to update it to maybe checksum the file as well (or perhaps just use a checksum for caching purposes rather than the gccxml output)? Thanks S

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