将 boost::python::numpy::ndarray 作为 boost::python 函数的（默认与否）参数传递？
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【中文标题】将 boost::python::numpy::ndarray 作为 boost::python 函数的（默认与否）参数传递？【英文标题】：Passing boost::python::numpy::ndarray as (default or not) argument of a boost::python function? 【发布时间】：2020-01-11 10:45:42 【问题描述】：是否可以将 boost::python::numpy::ndarray 作为 boost::python 函数的（默认或不）参数传递？
dummy 没有 ndarray。愚蠢的一个 ndarray 参数，但没有默认值。 silly 有一个 ndarray 作为默认值。
>> more dummy.cpp stupid.cpp silly.cpp
::::::::::::::
dummy.cpp
::::::::::::::
#include <boost/python.hpp>
namespace bp = boost::python;
int f(double x, double y=1.0) return (int)(x+y);;
BOOST_PYTHON_MODULE(dummy)
bp::def("f", f, ( bp::arg("x"), bp::arg("y")=1.0 ) );
::::::::::::::
stupid.cpp
::::::::::::::
#include <boost/python.hpp>
#include <boost/python/numpy.hpp>
namespace bp = boost::python;
namespace np = boost::python::numpy;
int f(np::ndarray x, double y=1.0) return (int)(x.shape(0)+y);;
BOOST_PYTHON_MODULE(stupid)
bp::def("f", f, ( bp::arg("x"), bp::arg("y")=1.0 ) );
::::::::::::::
silly.cpp
::::::::::::::
#include <boost/python.hpp>
#include <boost/python/numpy.hpp>
namespace bp = boost::python;
namespace np = boost::python::numpy;
int f(np::ndarray x, np::ndarray * y=nullptr) return (int)(y ? x.shape(0)+y->shape(0) : x.shape(0));;
BOOST_PYTHON_MODULE(silly)
bp::def("f", f, ( bp::arg("x"), bp::arg("y")=nullptr ) );
>> make
g++ -I /usr/include/python2.7 -o dummy.so -fPIC -shared dummy.cpp -lboost_python -lboost_numpy -lpython2.7
g++ -I /usr/include/python2.7 -o stupid.so -fPIC -shared stupid.cpp -lboost_python -lboost_numpy -lpython2.7
g++ -I /usr/include/python2.7 -o silly.so -fPIC -shared silly.cpp -lboost_python -lboost_numpy -lpython2.7
>> python
Python 2.7.17 (default, Oct 19 2019, 23:36:22)
[GCC 9.2.1 20191008] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import dummy; dummy.f(1)
2
>>> import numpy; import stupid; stupid.f(numpy.array([1, 2, 3]))
Segmentation fault
更新
尝试在f 中添加Py_Initialize(); np::initialize(); 没有成功
>> more stupid.cpp silly.cpp
::::::::::::::
stupid.cpp
::::::::::::::
#include <boost/python.hpp>
#include <boost/python/numpy.hpp>
namespace bp = boost::python;
namespace np = boost::python::numpy;
int f(np::ndarray x, double y=1.0)
Py_Initialize();
np::initialize();
return (int)(x.shape(0)+y);
;
BOOST_PYTHON_MODULE(stupid)
bp::def("f", f, ( bp::arg("x"), bp::arg("y")=1.0 ) );
::::::::::::::
silly.cpp
::::::::::::::
#include <boost/python.hpp>
#include <boost/python/numpy.hpp>
namespace bp = boost::python;
namespace np = boost::python::numpy;
int f(np::ndarray x, np::ndarray * y=nullptr)
Py_Initialize();
np::initialize();
return (int)(y ? x.shape(0)+y->shape(0) : x.shape(0));
;
BOOST_PYTHON_MODULE(silly)
bp::def("f", f, ( bp::arg("x"), bp::arg("y")=nullptr ) );
>> make
g++ -I /usr/include/python2.7 -o stupid.so -fPIC -shared stupid.cpp -lboost_python -lboost_numpy -lpython2.7
g++ -I /usr/include/python2.7 -o silly.so -fPIC -shared silly.cpp -lboost_python -lboost_numpy -lpython2.7
>> python
Python 2.7.17 (default, Oct 19 2019, 23:36:22)
[GCC 9.2.1 20191008] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy; import stupid; stupid.f(numpy.array([1, 2, 3]))
Segmentation fault
更新
好的，让它与调用 in BOOST_PYTHON_MODULE 一起工作。仍然使用默认参数 KO（silly 示例）。
>> more stupid.cpp silly.cpp
::::::::::::::
stupid.cpp
::::::::::::::
#include <boost/python.hpp>
#include <boost/python/numpy.hpp>
namespace bp = boost::python;
namespace np = boost::python::numpy;
int f(np::ndarray x, double y=1.0)
return (int)(x.shape(0)+y);
;
BOOST_PYTHON_MODULE(stupid)
Py_Initialize();
np::initialize();
bp::def("f", f, ( bp::arg("x"), bp::arg("y")=1.0 ) );
::::::::::::::
silly.cpp
::::::::::::::
#include <boost/python.hpp>
#include <boost/python/numpy.hpp>
namespace bp = boost::python;
namespace np = boost::python::numpy;
int f(np::ndarray x, np::ndarray * y=nullptr)
return (int)(y ? x.shape(0)+y->shape(0) : x.shape(0));
;
BOOST_PYTHON_MODULE(silly)
Py_Initialize();
np::initialize();
bp::def("f", f, ( bp::arg("x"), bp::arg("y")=nullptr ) );
>> make
g++ -I /usr/include/python2.7 -o stupid.so -fPIC -shared stupid.cpp -lboost_python -lboost_numpy -lpython2.7
g++ -I /usr/include/python2.7 -o silly.so -fPIC -shared silly.cpp -lboost_python -lboost_numpy -lpython2.7
>> python
Python 2.7.17 (default, Oct 19 2019, 23:36:22)
[GCC 9.2.1 20191008] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy; import stupid; stupid.f(numpy.array([1, 2, 3]))
4
>>> import numpy; import silly; silly.f(numpy.array([1, 2, 3]))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: No to_python (by-value) converter found for C++ type: decltype(nullptr)
解决方法
>> more silly.cpp
#include <boost/python.hpp>
#include <boost/python/numpy.hpp>
namespace bp = boost::python;
namespace np = boost::python::numpy;
int f(np::ndarray x, bp::object y)
np::ndarray yy = np::array(bp::list());
if (!y.is_none()) yy = bp::extract<np::ndarray>(y);
return (int)(x.shape(0)+yy.shape(0));
;
BOOST_PYTHON_MODULE(silly)
Py_Initialize();
np::initialize();
bp::def("f", f, ( bp::arg("x"), bp::arg("y") ) );
>> make
g++ -I /usr/include/python2.7 -o silly.so -fPIC -shared silly.cpp -lboost_python -lboost_numpy -lpython2.7
>> python
Python 2.7.17 (default, Oct 19 2019, 23:36:22)
[GCC 9.2.1 20191008] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy; import silly; silly.f(numpy.array([1, 2, 3]), numpy.array([1, 2]))
5
>>> import numpy; import silly; silly.f(numpy.array([1, 2, 3]), None)
3
【问题讨论】：
【参考方案1】：为了能够使用numpy，首先初始化Python运行时和numpy模块：
Py_Initialize();
np::initialize();
未能调用这些会导致分段错误。
================================================ =========================
对于silly.cpp，不需要解决方法。这是实现：
#include <boost/python.hpp>
#include <boost/python/numpy.hpp>
namespace bp = boost::python;
namespace np = boost::python::numpy;
int f(np::ndarray x, np::ndarray y = np::array(bp::list()) )
return (int)(x.shape(0)+y.shape(0));
;
BOOST_PYTHON_MODULE(silly)
Py_Initialize();
np::initialize();
bp::def("f", f, ( bp::arg("x"), bp::arg("y") = np::array(bp::list()) ) );
以及测试结果：
>>> import numpy, silly; silly.f(numpy.array([1, 2, 3]), numpy.array([1, 2]))
5
>>> import numpy, silly; silly.f(numpy.array([1, 2, 3]))
3
【讨论】：
当然，错过了：尝试在f 中添加这些调用但没有成功...
好的，让它与调用 in BOOST_PYTHON_MODULE 一起工作。仍然使用默认参数 KO（silly 示例）
@FGH 我已经删除了 silly.cpp 中的解决方法 - 请参阅我更新的答案。以上是关于将 boost::python::numpy::ndarray 作为 boost::python 函数的（默认与否）参数传递？的主要内容，如果未能解决你的问题，请参考以下文章
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