Mailman 3 January 2018 - Cplusplus-sig

Copying string values to ndarray using Boost.Python
by Mohan Varma Jan. 31, 2018

Jan. 31, 2018

I have been trying to create an ndarray in C++ using Boost.Python while creating a Python module. The ndarray object is created using a composite dtype with an int value column, a 32-byte string column and a float value column. I am able to set the values for int and float columns and access them in Python. I am not sure on how to set the string column values in C++. Here is the synopsis of my code, I believe it explains the problem fairly well. Any help in this regard is greatly appreciated. struct Test { int id; std::string name; float value; }; std::vector<Test> test_values; // namespace bp = boost::python; namespace np = boost::python::numpy; // // bp::tuple shape = bp::make_tuple(test_values.size()); bp::list list_for_dtype; list_for_dtype.append(bp::make_tuple("id",np::dtype::get_builtin<int>())); list_for_dtype.append(bp::make_tuple("name", np::dtype(bp::str("U32")))); list_for_dtype.append(bp::make_tuple("value",np::dtype::get_builtin<float>())); np::dtype custom_dtype = np::dtype(list_for_dtype); int item_size = custom_dtype.get_itemsize(); np::ndarray values_array = np::zeros(shape, custom_dtype); char * dest_ptr = (char *) values_array .get_data(); for (size_t i = 0; i < test_values.size(); ++i) { memcpy((void *) dest_ptr, &test_values[i].id, sizeof(int)); dest_ptr += sizeof(int); // How do I copy the string value to ndarray buffer? //bp::str bpname(&test_values[i].name); //memcpy((void *) dest_ptr, bpname.ptr(), sizeof(float)); dest_ptr += 32 * 4; memcpy((void *) dest_ptr, &test_values[i].value, sizeof(float)); dest_ptr += sizeof(float); } Thank you, Mohan.

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How can I get access to "argv/argc" command line in a boost python c++ extension?
by Liam Herron Jan. 29, 2018

Jan. 29, 2018

So I have a boost python extension C++ library. I would like to access the "python commandline" in C++ without having to pass in the "sys.argv" into my C++ extension. Is there a way to do this? Include some boost python header and read it from some init variables or something? e.g. python someScript.py A B C 1 2 3 ////////////////////////////////////////////////////////////////////////// class_<DummyCppClass> ("DummyCppClass", "DummyCppClass obj", init<>()) .def("printCmdLine", &DummyCppClass::printCmdLine) ; ////////////////////////////////////////////////////////////////////////// #include <string> #include <iostream> std::string DummyCppClass::printCmdLine() const { std::cout << "Prog: " << HERE_argv[0] << ", Arg1: " << HERE_argv[1] << std::endl; } ////////////////////////////////////////////////////////////////////////// ============================================================================================= Email transmissions can not be guaranteed to be secure or error-free, as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore does not accept liability for any errors or omissions in the contents of this message which arise as a result of email transmission. In addition, the information contained in this email message is intended only for use of the individual or entity named above. If the reader of this message is not the intended recipient, or the employee or agent responsible to deliver it to the intended recipient, you are hereby notified that any dissemination, distribution,or copying of this communication, disclosure of the parties to it, or any action taken or omitted to be taken in reliance on it, is strictly prohibited, and may be unlawful. If you are not the intended recipient please delete this email message. ==============================================================================================

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Boost-Python: Inconsistent shared_ptr use-count since Boost 1.63
by Charlie Dyson Jan. 26, 2018

Jan. 26, 2018

I believe the following behaviour changes in 1.63 judging by the ChangeLog, though unfortunately I can only test 1.60 vs 1.66 at the moment. Using Enterprise Linux 7 with gcc 7.2. Consider this module: #include <boost/python.hpp> #include <iostream> #include <memory> namespace bp = boost::python; struct X { ~X () { std::cout << "Bye bye" << std::endl; } }; BOOST_PYTHON_MODULE (pymodule) { bp::class_<X, std::shared_ptr<X>> x_wrap ("X"); // Not needed in newer boost bp::register_ptr_to_python<std::shared_ptr<X>> (); auto x1 = std::make_shared<X> (); auto x2 = bp::extract<std::shared_ptr<X>> (bp::object (x1)) (); // On a newer boost: use counts are not the same std::cout << x1.get () << ": "<< x1.use_count () << std::endl; // 2 std::cout << x2.get () << ": "<< x2.use_count () << std::endl; // 1 :( } For the older Boost, the reference counts are both two, but they are 2 and 1 respectively in the newer Boost. Is this expected? I wonder if there's some cleverness involving x2 somehow pointing to a BP object that in turn points to x1. Curiously X appears to only be destructed once, so it doesn't look like UB. Where it bites me is cleanup time. If I add the following to the end of the module, I get a segfault: static std::vector<std::shared_ptr<X>> v {x2}; Backtrace as follows: #0 subtype_dealloc (self=0x7ffff7e24050) at Objects/typeobject.c:955 #1 0x00007fffef9dfb59 in xdecref<_object> (p=<optimized out>) at ./boost/python/refcount.hpp:38 #2 reset (this=0x6c1f30) at ./boost/python/handle.hpp:222 #3 boost::python::converter::shared_ptr_deleter::operator() (this=0x6c1f30) at libs/python/src/converter/builtin_converters.cpp:35 #4 0x00007ffff7ff563a in _M_release (this=0x6c1f20) at .../bits/shared_ptr_base.h:154 #5 ~__shared_count (this=<optimized out>, __in_chrg=<optimized out>) at .../bits/shared_ptr_base.h:684 #6 ~__shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at .../bits/shared_ptr_base.h:1123 #7 ~shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at .../bits/shared_ptr.h:93 #8 _Destroy<std::shared_ptr<X> > (__pointer=<optimized out>) at .../bits/stl_construct.h:98 #9 __destroy<std::shared_ptr<X>*> (__last=<optimized out>, __first=0x678920) at .../bits/stl_construct.h:108 #10 _Destroy<std::shared_ptr<X>*> (__last=<optimized out>, __first=<optimized out>) at .../bits/stl_construct.h:137 #11 _Destroy<std::shared_ptr<X>*, std::shared_ptr<X> > (__last=0x678930, __first=<optimized out>) at .../bits/stl_construct.h:206 #12 std::vector<std::shared_ptr<X>, std::allocator<std::shared_ptr<X> > >::~vector (this=0x7ffff7ff7a60 <init_module_pymodule()::v>, __in_chrg=<optimized out>) at .../bits/stl_vector.h:434 #13 0x00007ffff6d24e69 in __run_exit_handlers () from /lib64/libc.so.6 #14 0x00007ffff6d24eb5 in exit () from /lib64/libc.so.6 #15 0x00007ffff6d0db1c in __libc_start_main () from /lib64/libc.so.6 #16 0x00000000004007a1 in _start () Is this a new behaviour change, or a bug, or was it always dangerous and I have just been lucky until now? Many thanks, Charlie

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