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我正在使用 pybind11 为我无法更改其源的 C++ 库创建 python 绑定。它包含一个定义具有右值引用参数(例如T &&val)的成员函数的类。我无法创建与具有右值引用参数的成员函数的绑定,但绑定到具有相同参数的非成员函数按预期工作。

一个简化的示例如下所示:

struct Foo {
    // Cannot create a pybinding for this method.
    void print_ref(int &&v) const {
            std::cout << "Foo::print_ref(" <<  to_string(v) << ")" <<std::endl;
    }
};
// Pybinding for standalone function works as expected.
void print_ref(int&& val) {
        std::cout << "print_ref(" << to_string(val) << ")" << std::endl;
};

pybind11 代码如下所示:

PYBIND11_MODULE(refref, m) {
    py::class_<Foo>(m, "Foo")
    // Both of these attempts to create a pybinding FAILs with same error.
    .def("print_ref", &Foo::print_ref)
    .def("print_ref", (void (Foo::*) (int&&)) &Foo::print_ref);
    // This pybinding of standalone function is SUCCESSful.
    m.def("print_ref", &print_ref);
}

第一次绑定尝试的编译错误是:

pybind11/bin/../include/site/python3.4/pybind11/pybind11.h:79:80: error: rvalue reference to type 'int' cannot bind to lvalue of type 'int'
        initialize([f](const Class *c, Arg... args) -> Return { return (c->*f)(args...); },
                                                                               ^~~~
pybind11/bin/../include/site/python3.4/pybind11/pybind11.h:1085:22: note: in instantiation of function template specialization 'pybind11::cpp_function::cpp_function<void, Foo, int &&,
      pybind11::name, pybind11::is_method, pybind11::sibling>' requested here
        cpp_function cf(method_adaptor<type>(std::forward<Func>(f)), name(name_), is_method(*this),
                     ^
refref.cpp:31:3: note: in instantiation of function template specialization 'pybind11::class_<Foo>::def<void (Foo::*)(int &&) const>' requested here
        .def("print_ref", &Foo::print_ref);

关于我可能做错了什么的任何想法?由于它适用于非成员函数,我倾向于怀疑 pybind11 问题,但我想我会先在这里检查。

4

1 回答 1

2

确实,问题来自于rvalues。我从这个 SO 答案这篇博文中学到了很多东西。有一个很好的解决方法:您可以创建一个包装类,它将调用重定向到您无法更改的 C++ 库,并注意rvalue语义std::move

#include <iostream>
#include <pybind11/pybind11.h>
#include <pybind11/numpy.h>

namespace py = pybind11;

struct Foo {
    void print_ref(int&& v) const {
            std::cout << "Foo::print_ref("  <<  +v << ")" <<std::endl;
    }
};


// This class will interface between PyBind and your library
class Foo_wrap{
private:
  Foo _mimu;
public:
  void print_ref(int v) const{
    _mimu.print_ref(std::move(v));
  }
};



PYBIND11_MODULE(example, m) {
     py::class_<Foo_wrap>(m, "Foo_wrap")
     .def(py::init())
     .def("print_ref", &Foo_wrap::print_ref);
}

你可以用 Python 调用

import example as fo

wr = fo.Foo_wrap()
wr.print_ref(2)
于 2018-05-03T13:15:30.250 回答