How can I use Boost::Python to add a method to an exported class without modifying the base class?
I have a class in C++ that I can't modify. However, that class holds an std::list<> of items that I need to be able to access in a Python extension. Since Boost::Python doesn't seem to have a built-in conversion between an std::list and a Python list, I was hoping to be able to write a method in C++ that could do this conversion for me and later, when I am mapping the C++开发者_如何学运维 classes to Python classes, I could attach this method.
I would prefer if I could just call the method like
baseClassInstance.get_std_list_of_items_as_python_list()
To answer the question in a more general way, you can attach any c++ function that has the right signature to the python export in the class_ declaration.
assume a class foo:
struct foo
{
//class stuff here
}
You can define a free function that takes a reference to foo as the first argument:
int do_things_to_a_foo(foo& self, int a, std::string b, other_type c)
{
//Do things to self
}
And export it just like a member of foo:
class_<foo>("foo")
...
.def("do_things_to_a_foo", &do_things_to_a_foo)
...
;
Boost provides a helper to wrap iterators which is documented here: http://www.boost.org/doc/libs/1_42_0/libs/python/doc/v2/iterator.html
The example hear the end of that page worked for me, you just need to explicitly create the conversion, for example:
class_<std::list<Item> >("ItemList")
.def("__iter__", iterator<std::list<Item> >());
To modify the C++ class without changing it, I am in the habit of creating a thin wrapper that subclasses the real class. This makes a nice place to separate out all the crud that makes my C++ objects feel comfortable from Python.
class Py_BaseClass : public BaseClass {
public:
std::list<Item> & py_get_items();
}
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