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[英]How to expose a c++ function taking variable arguments in boost python
[英]Expose C++ member function that has std::function as argument with boost::python
我有一个包含属性的类,该属性是std :: function。 我使用成员函数设置此属性的值,因此该类如下所示:
class ClassName
{
public:
void SetCallbackFunction(std::function<void (int i)> callbackFun) {
m_callbackFunction = callbackFun;
}
protected:
std::function<void (int i)> m_callbackFunction;
};
我需要将该类公开给Python,当然,我需要公开SetCallbackFunction
函数。 如何使用boost :: python做到这一点?
由于Python对象既是Callable对象又是CopyConstructible对象,所以最简单的方法是将辅助函数公开为SetCallbackFunction
,该函数接受boost::python::object
,然后委托给实际的SetCallbackFunction
函数:
void ClassName_SetCallbackFunction_aux(ClassName& self, boost::python::object object)
{
self.SetCallbackFunction(object);
}
BOOST_PYTHON_MODULE(example)
{
namespace python = boost::python;
python::class_<ClassName>("ClassName", python::init<>())
.def("set_callback", &ClassName_SetCallbackFunction_aux)
// ...
;
}
当ClassName::SetCallbackFunction
直接公开给Python并调用时,Boost.Python将在运行时搜索其注册表,以查找Python转换器中的std::function<void (int)>
。 由于尚未明确注册此转换,因此Boost.Python将无法分派函数调用。 辅助函数避免了这种运行时转换检查,并从boost::python::object
构造了一个std::function<void (int)>
boost::python::object
,因为boost::python::object
既可调用,也可进行CopyConstructible。
这是一个示例, 演示使用辅助函数将Python对象分配为回调:
#include <functional> // std::function
#include <boost/python.hpp>
// Legacy API.
class spam
{
public:
void SetCallbackFunction(std::function<void (int)> callback)
{
callback_ = callback;
}
void perform(int x)
{
callback_(x);
}
private:
std::function<void (int)> callback_;
};
BOOST_PYTHON_MODULE(example)
{
namespace python = boost::python;
// Expose spam.
python::class_<spam>("Spam", python::init<>())
// Use an auxiliary function to set Python callbacks.
.def("set_callback", +[](spam& self, boost::python::object object) {
self.SetCallbackFunction(object);
})
.def("perform", &spam::perform)
;
}
互动用法:
>>> import example
>>> called = False
>>> def perform_x(x):
... assert(42 == x)
... global called
... called = True
...
>>> spam = example.Spam()
>>> spam.set_callback(perform_x)
>>> assert(not called)
>>> spam.perform(42)
>>> assert(called) # Verify callback was invoked
>>> spam.set_callback(lambda: None)
>>> try:
... spam.perform(42)
... assert(False) # Verify callback fails (the lambda accepts no args)
... except TypeError:
... pass
...
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