How to Properly Expose Enum Comparison Operators to Python Using Boost.Python?

[MasterBe]

I'm trying to expose a C++ enum and its comparison operators to Python using Boost.Python. I've defined the enum and comparison operators as shown in the code below:

///////color.hpp
enum Color {
    Red,
    Green,
    Blue
};

bool operator<(const Color c1, const Color c2)
{
    return static_cast<int>(c1) < static_cast<int>(c2);
}

///////color_python.hpp
#include <boost/python.hpp>
#include <color.hpp>

bool ltColor(const Color& c1, const Color& c2)
{
    return c1 < c2;
}

BOOST_PYTHON_MODULE(my_module)
{
    using namespace boost::python;

    enum_<Color>("Color")
        .value("Red", Red)
        .value("Green", Green)
        .value("Blue", Blue);

    // Expose comparison operators
    def("__lt__", &ltColor)
    //other operators i.e. __le__ ...
    ;
}

This compiles fine but looks like python defines these comparison automatically hence does not care about my definitions at all and even if I throw in ltColor it does not throw in jupyter for example.

Still when I include the color.hpp in another file user.cpp, the code does not even compile:

///////user.cpp
#include <color.hpp>

void my_function()
{
   //...
}

I get: error LNK2005: "bool __cdecl operator<(enum Color,enum Color)" (??....) already defined in color_python.cpp.obj

[MasterBe]

Solution: The operator has to be static