c++ - Boost.python 继承自包装类

Question

我在使用 boost.python 为现有库创建 python 绑定(bind)时遇到了问题。场景如下:

#include<boost/python.hpp>

namespace bp = boost::python;

struct Base {
    std::stringstream _myString;
    Base() { };
    Base(const Base& base) { _myString<<base._myString.str(); }

    void getString(std::stringstream& some_string) {
        _myString.str("");
        _myString<<some_string.str();
        std::cout<<"Got string: \""<<_myString.str()<<"\""<<std::endl;
    }
};

struct BaseWrapper : Base,
                     bp::wrapper<Base>
{
    BaseWrapper() :
        Base(),
        bp::wrapper<Base>() { };

    BaseWrapper(const Base& base) :
        Base(base),
        bp::wrapper<Base>() { };

    void getString(bp::object pyObj) {
        std::string strLine = bp::extract<std::string>(pyObj);
        std::stringstream sstrLine;
        sstrLine<<strLine;
        Base::getString(sstrLine);
    }
};

struct Derived : Base
{
    Derived() : Base() { };
    Derived(const Derived& derived) : Base() { _myString<<derived._myString.str(); };
};

struct DerivedWrapper : Derived,
                        bp::wrapper<Derived>
{
    DerivedWrapper() :
        Derived(),
        bp::wrapper<Derived>() { };

    DerivedWrapper(const Derived derived) :
        Derived(derived),
        bp::wrapper<Derived>() { };
};

BOOST_PYTHON_MODULE(testInheritance){
    bp::class_<BaseWrapper>("Base")
        .def("getString", &BaseWrapper::getString);

    bp::class_<DerivedWrapper, bp::bases<Base> >("Derived");
}

(抱歉代码块太长，这是我能想到的最小示例。)

您可以看到我必须覆盖 BaseWrapper 中的 getString() 方法，以便它可以处理 Python 字符串，这部分工作正常:

>>> import testInheritance
>>> base = testInheritance.Base()
>>> base.getString("bla")
Got string: "bla"
>>>

当我尝试从 Derived 的实例调用 getString 时，问题就出现了:

>>> derived = testInheritance.Derived()
>>> derived.getString("bla")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
Boost.Python.ArgumentError: Python argument types in
    Base.getString(Derived, str)
did not match C++ signature:
    getString(BaseWrapper {lvalue}, boost::python::api::object)
>>>

我能理解这里出了什么问题，但我不知道如何解决。如果有任何帮助，我将不胜感激!

最好的问候，爱 bean

Answer 1

问题是，DerivedWrapper 与 BaseWrapper 没有关系。因此 DerivedWrapper 需要提供它自己的 python 改编的 void getString(bp::object pyObj) 实现。

所以让它工作的一种方法是这样的:

struct DerivedWrapper : Derived,
                        bp::wrapper<Derived>
{
    DerivedWrapper() :
        Derived(),
        bp::wrapper<Derived>() { };

    DerivedWrapper(const Derived derived) :
        Derived(derived),
        bp::wrapper<Derived>() { };

    void getString(bp::object pyObj) {
        std::string strLine = bp::extract<std::string>(pyObj);
        std::stringstream sstrLine;
        sstrLine<<"(from DerivedWrapper) "<<strLine;
        Derived::getString(sstrLine);
    }
};

[...]

    bp::class_<DerivedWrapper, bp::bases<Base> >("Derived")
        .def("getString", &DerivedWrapper::getString);

和输出

base = testInheritance.Base()
base.getString("bla")

derived = testInheritance.Derived()
derived.getString("blub")

符合预期

Got string: "bla"
Got string: "(from DerivedWrapper) blub"