Cppyy pythonization with templates?

Question

Is there a way to write pythonizations in cppyy that work for all templates?

I have a class in C++ that requires a template

template <typename TValueType>
Bound<TValueType> Bound<TValueType>::buildInclusiveBound(TValueType value) {
  return Bound<TValueType>{BoundCategory::Inclusive, value};
}

I noticed that when I was writing a pythonization of this function, this did not work

import cppyy.gbl as Cpp

Cpp.Bound.__str__ = lambda self: "test"

but

import cppyy.gbl as Cpp

Cpp.Bound['double'].__str__ = lambda self: "test"

did.

@WimLavrijsen do you have any suggestions? – shouriha May 08 '23 at 18:17 — shouriha, May 08 '23 at 18:17

score 1 · Accepted Answer · answered May 08 '23 at 20:23

Bound isn't a class just as much as e.g. std::vector isn't, so there's no Python proxy to Pythonize. Easiest solution is probably a name check using a pre-registered pythonizor. Example:

import cppyy

cppyy.cppdef(r"""\
namespace MyNamespace {
template<typename T>
class MyClass {
public:
    MyClass(T t) : m_data(t) {}
    T m_data;
};
}""")

def pythonize_myclass(klass, name):
    if 'MyClass' in name:
        klass.__str__ = lambda x: str(x.m_data)

cppyy.py.add_pythonization(pythonize_myclass, 'MyNamespace')

mi = cppyy.gbl.MyNamespace.MyClass[int](42)
print(mi)

md = cppyy.gbl.MyNamespace.MyClass['double'](42.)
print(md)

Cppyy pythonization with templates?

1 Answers1