如何解决自己的字符串用法
| 我有自己的字符串类,我想将其导出到python(带有boost.python)中,并用作本地字符串。我为此编写了转换器。 首先是导出我的字符串:bp::class_<CL_StringRef8>(\"CL_StringRef8\",bp::init<const std::string&>())
.def(\"CStr\",&CL_StringRef8::c_str);
转换器来自默认教程,但具有我的类型:
// CL_StringRef8 → Python string --------------------------------------
struct cl_stringref8_to_python_str
{
static PyObject* convert(CL_StringRef8 const& s)
{
return boost::python::incref(boost::python::object(s.c_str()).ptr());
}
};
// Python string → CL_StringRef8 --------------------------------------
struct cl_stringref8_from_python_str
{
cl_stringref8_from_python_str()
{
bp::converter::registry::push_back(
&convertible,&construct,boost::python::type_id<CL_StringRef8>()
);
}
static void* convertible(PyObject* obj_ptr)
{
if (!PyString_Check(obj_ptr)) return 0;
return obj_ptr;
}
static void construct(PyObject* obj_ptr,bp::converter::rvalue_from_python_stage1_data* data)
{
const char* value = PyString_AsString(obj_ptr);
if (value == 0) bp::throw_error_already_set();
void* storage = ((bp::converter::rvalue_from_python_storage<CL_StringRef8>*)data)->storage.bytes;
new (storage) CL_StringRef8(value);
data->convertible = storage;
}
};
现在,据我所知,我可以从python中调用带有参数which2 takes的c ++函数,但是我有一个代码:
print GetMyStringObject()
data = float(GetMyStringObject())
# ==>
<CL_StringRef object at 0x7fd15dfd9de8>
TypeError: float() argument must be a string or a number
据我了解,我必须为CL_StringRef8
导出str()
方法,但是我不能这样做:
bp::class_<CL_StringRef8>(\"CL_StringRef8\",&CL_StringRef8::c_str)
.def(bp::self_ns::str(bp::self_ns::self));
最后一行调用错误:
/usr/include/boost/lexical_cast.hpp: In member function ‘bool boost::detail::lexical_stream<Target,Source,Traits>::operator<<(const Source&) [with Target = std::basic_string<char>,Source = CL_StringRef8,Traits = std::char_traits<char>]’:
/usr/include/boost/lexical_cast.hpp:1151:13: instantiated from ‘Target boost::detail::lexical_cast(typename boost::call_traits<Source>::param_type,CharT*,std::size_t) [with Target = std::basic_string<char>,bool Unlimited = true,CharT = char,typename boost::call_traits<Source>::param_type = const CL_StringRef8&,std::size_t = long unsigned int]’
/usr/include/boost/lexical_cast.hpp:1174:77: instantiated from ‘Target boost::lexical_cast(const Source&) [with Target = std::basic_string<char>,Source = CL_StringRef8]’
/usr/include/boost/python/operators.hpp:357:1: instantiated from ‘static PyObject* boost::python::detail::operator_1<(boost::python::detail::operator_id)19u>::apply<T>::execute(boost::python::detail::operator_1<(boost::python::detail::operator_id)19u>::apply<T>::self_t&) [with T = CL_StringRef8,PyObject = _object,boost::python::detail::operator_1<(boost::python::detail::operator_id)19u>::apply<T>::self_t = CL_StringRef8]’
/usr/include/boost/python/operators.hpp:152:11: instantiated from ‘void boost::python::detail::operator_<id,L,R>::visit(ClassT&) const [with ClassT = boost::python::class_<CL_StringRef8>,boost::python::detail::operator_id id = (boost::python::detail::operator_id)19u,L = boost::python::detail::not_specified,R = boost::python::detail::not_specified]’
/usr/include/boost/python/def_visitor.hpp:31:9: instantiated from ‘static void boost::python::def_visitor_access::visit(const V&,classT&) [with V = boost::python::def_visitor<boost::python::detail::operator_<(boost::python::detail::operator_id)19u> >,classT = boost::python::class_<CL_StringRef8>]’
/usr/include/boost/python/def_visitor.hpp:67:9: instantiated from ‘void boost::python::def_visitor<DerivedVisitor>::visit(classT&) const [with classT = boost::python::class_<CL_StringRef8>,DerivedVisitor = boost::python::detail::operator_<(boost::python::detail::operator_id)19u>]’
/usr/include/boost/python/class.hpp:225:9: instantiated from ‘boost::python::class_<T,X1,X2,X3>::self& boost::python::class_<T,X3>::def(const boost::python::def_visitor<Derived>&) [with Derived = boost::python::detail::operator_<(boost::python::detail::operator_id)19u>,W = CL_StringRef8,X1 = boost::python::detail::not_specified,X2 = boost::python::detail::not_specified,X3 = boost::python::detail::not_specified,boost::python::class_<T,X3>::self = boost::python::class_<CL_StringRef8>]’
/home/ockonal/Workspace/Themisto/src/Scripts/Core/TypesConverters.cpp:375:49: instantiated from here
/usr/include/boost/lexical_cast.hpp:595:48: error: cannot bind ‘std::basic_ostream<char>’ lvalue to ‘std::basic_ostream<char>&&’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.0/../../../../include/c++/4.6.0/ostream:581:5: error: initializing argument 1 of ‘std::basic_ostream<_CharT,_Traits>& std::operator<<(std::basic_ostream<_CharT,_Traits>&&,const _Tp&) [with _CharT = char,_Traits = std::char_traits<char>,_Tp = CL_StringRef8]’
ps和是的,我没有忘记将转换器注册到python中。
解决方法
为了使
.def(bp::self_ns::str(bp::self_ns::self));
行工作,您需要为您的课程定义流操作符。
std::ostream & operator<<(std::ostream & os,const CL_StringRef8 &s)
{ os << s.c_str(); return os; }
在不需要流运算符的情况下定义str()方法的另一种方法是:
.def(\"__str__\",&CL_StringRef8::c_str)
虽然,我更喜欢只做repr()方法,然后在需要时由str()使用
.def(\"__repr__\",&CL_StringRef8::c_str)
所有这些仍然无法使float()在Python中工作,因为它期望一个字符串(即使支持__str__也不是一个对象),一个浮点数或一个支持__float__的对象。
我们可以通过在您的c_str()方法周围绑定一个lexical_cast来实现后者:
#include <boost/lexical_cast.hpp>
#include <boost/mpl/vector.hpp>
接着
.def(\"__float__\",bp::make_function(
boost::bind(&boost::lexical_cast<float,CL_StringRef8>,_1),bp::default_call_policies(),boost::mpl::vector<float,CL_StringRef8>()));
现在您可以在Python中执行此操作:
>>> a = CL_StringRef8(\"1.234\")
>>> print a
1.234
>>> float(a) * 2
2.468
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