Mailman 3 April 2004 - Cplusplus-sig

Construct for c++ class with reference
by Neal D. Becker April 20, 2004

April 20, 2004

How should I wrap this (simplified example): struct X { X (int& _x) : x (_x) {} int& x; };

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a python property being a reference
by Alex April 20, 2004

April 20, 2004

add_property("toto", &CToto::get_toto) with CToto::get_toto returning an object reference it doesn't work caus it needs a "return value policy" how can i give a return value policy in add_property like in def ? thanks Alex Legrand

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creating character arrays in Boost.Python
by Faheem Mitha April 20, 2004

April 20, 2004

Dear People, If I want to create a character array in C++ in Boost.Python, along similar lines to Python's numarray.strings.array(itemsize,shape), is there a way to do it? The collection of factory functions in <boost/python/numeric.hpp> look relevant, but I am not sure what the correct syntax would be. For example, what should I set for Buffer? Thanks. Faheem.

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help building hello world example on Debian
by Faheem Mitha April 20, 2004

April 20, 2004

Dear People, I have spent the last couple of hours trying to understand how to use bjam so as to build the `hello world' tutorial example for boost-python. I have not succeeded. I'm running Debian sarge. Debian seems me to want to use boost-python 1.30.2, though I also have 1.31 installed. I have also installed bjam. The Jamfile from the hello world example appears below. How should I modify this to work on my system? Alternatively, I'd be happy with a regular Makefile. I would prefer not to have to do extensive configuration of other files, and I'd also prefer not to have to modify the jamfile if I moved it to a different location in the directory hierarchy. Can these preferences be satisfied? When running bjam on the script below I get the following. bjam Unable to load Boost.Build: could not find build system. --------------------------------------------------------- /home/faheem/wc/boost/example/boost-build.jam attempted to load the build system by invoking 'boost-build ../../../tools/build/v1 ;' but we were unable to find "bootstrap.jam" in the specified directory or in BOOST_BUILD_PATH (searching /home/faheem/wc/boost/example/../../../tools/build/v1, /usr/share/boost-build). I have tried reading the documentation but it seems very complicated and I just get more confused. Some guidance would be appreciated. Faheem. ***************************************************************** # Hello World Example from the tutorial # [Joel de Guzman 10/9/2002] # Specify our location in the boost project hierarchy subproject libs/python/example/tutorial ; # Include definitions needed for Python modules import python ; extension hello # Declare a Python extension called hello : hello.cpp # source <dll>../../build/boost_python # dependencies ;

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build-in arrray C API
by Dmitri Mouromtsev April 19, 2004

April 19, 2004

Hello all, I want to use build-in array module in embedded Python. But there is no API for this module. How can I use it? thanks.

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Redirecting stdout/stderr
by koestler April 19, 2004

April 19, 2004

Hi, I am using Python as an embedded scripting language within a wxWindows application. To redirect the stdout/stderr I'm using the following module: import sys class StdoutCatcher: def __init__(self): self.data = '' def write (self,stuff): self.data = self.data + stuff def redirectStdout(): sys.stdout = StdoutCatcher ( ) def redirectStderr(): sys.stderr = StdoutCatcher ( ) def getStdout(): return sys.stdout.data def getStderr(): return sys.stderr.data This gives me access to the interpreter's I/O if the I/O has happened within the module. Now I want the user to be able to interactively type in Python commands using PyRun_SimpleString. Is there a way to access the stdout/stderr that way? Thanks for your help. Ca folks

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How to start using C++ from Python.
by Ajay Gupta April 16, 2004

April 16, 2004

Hi, I need to work on project, where I am planning to call C++ from python. Any help would be highly appreciated. Ajay Gupta Application Infrastructure 60 Wall Street, 9th Floor, New York, NY 10005 Office: (212) 250 0958 Cell : (917) 710 6027 -- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

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.def & virtual functions with default implementations
by Matthias Baas April 16, 2004

April 16, 2004

Hi, in the tutorial there's an example how to wrap virtual methods that have default implementations (http://www.boost.org/libs/python/doc/tutorial/doc/virtual_functions_with_de…). I think I've understood the principle, however I don't quite understand this line: .def("f", &Base::f, &BaseWrap::default_f) Why do I have to provide &Base::f? Why isn't it enough to write .def("f", &BaseWrap::default_f) This would already have the effect that calling f() from Python will actually call the default implementation instead of recursively calling the dispatch function. And when f() is called from C++ the dispatch function will be called because it overrides the original function. If all this is correct, then why does Boost.Python need to know about &Base::f? Actually, this latter approach is used in the example in the Wiki which looks like this: .def("greet", &hello_callback::default_greet); (http://www.python.org/cgi-bin/moinmoin/boost_2epython_2fOverridableVirtualF…) So what is actually the difference of those two types of definitions? And which tutorial is correct? - Matthias -

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vector_indexing_suite override question
by Neal D. Becker April 16, 2004

April 16, 2004

I'm trying to wrap my new Ring class, which is a vector-like class. I was hoping to use vector_indexing_suite but override one operator. template<class Container> struct my_indexing_suite : public vector_indexing_suite<Container> { typedef typename vector_indexing_suite<Container>::index_type index_type; static index_type convert_index(Container& container, PyObject* i_) { throw ("help"); } }; BOOST_PYTHON_MODULE(Ring_wrap) { class_<Ring<int> >("RI") .def(init<size_t>()) .def(init<const Ring<int>&>()) .def (my_indexing_suite<Ring<int> >()) .def ("Shift", &Ring<int>::Shift) ; } This doesn't seem to work. my_indexing_suite::convert_index is apparantly never called. Any suggestions? BTW, anyone know how to test this with gdb? I tried gdb /usr/bin/python, run, import, ^C-c, then try to set a breakpoint in my code, but gdb doesn't seem to know how to set the breakpoint in the shared lib code. Is this cause python was not compiled with -g?

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bug in numarray (using take with character arrays) possibly affecting boost.python
by Faheem Mitha April 15, 2004

April 15, 2004

See http://sourceforge.net /tracker/index.php?func=detail&aid=935882&group_id=1369&atid=450446 For convenience the bug report is reproduced below. The following wrapper to boost.python gives the same behaviour described in the bug report, so I'm guessing that if boost.python used the numarray implementation of `take' the bug will be there too. In neither the numarray version or the boost.python version of take does this bug show up for arrays of numerical values. **************************************************************** Boost.Python wrapper to take (in <boost/python/numeric.hpp>). **************************************************************** // Version of take obtained by calling Boost.Python take. numeric::array mytake(numeric::array& y, const tuple& ind, int i) { return extract<numeric::array>(y.take<tuple>(ind,i)); } **************************************************************** Faheem. ************************************************************************* Bug report. ************************************************************************* In [22]: import numarray.strings as str In [23]: import numarray In [24]: s = str.array(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i'],shape=(3,3)) In [25]: numarray.take(s,(1,2),axis=1) --------------------------------------------------------------------------- ValueError Traceback (most recent call last) /home/faheem/wc/corrmodel/boost/<console> /usr/lib/python2.3/site-packages/numarray/ufunc.py in take(array, indices, axis, outarr, clipmode) 1779 raise ValueError("indices must be a sequence") 1780 work = _gen.swapaxes(array, 0, axis) -> 1781 work = work._take((indices,), outarr=outarr, clipmode=clipmode) 1782 return _gen.swapaxes(work, 0, axis) 1783 else: /usr/lib/python2.3/site-packages/numarray/generic.py in _take(self, indices, **keywds) 795 def _take(self, indices, **keywds): 796 indices = list(indices) --> 797 impliedShape, N = _takeShape(self, indices) 798 result = self._clone(shape=impliedShape) 799 indices = self._fix_pt_indices(indices) /usr/lib/python2.3/site-packages/numarray/generic.py in _takeShape(scattered, indexArrays) 133 nShape = scattered._shape[-leftOver:] 134 if scattered.isbyteswapped() or not scattered.iscontiguous(): --> 135 raise ValueError("Invalid destination array: partial indices require contiguous non-byteswapped destination") 136 else: 137 N = scattered._itemsize ValueError: Invalid destination array: partial indices require contiguous non-byteswapped destination

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