Wrap enum class for cython

Question

I am trying to wrap an enum class in a c++ header file for use in a cython project.I have googled around and can not find out how to achieve this - is it supported?

Answer 1

CPP class

enum class Color {red, green = 20, blue}; 

Definition of type

cdef extern from "colors.h":
  cdef cppclass Color:
    pass

Definition of color types

cdef extern from "colors.h" namespace "Color":
  cdef Color red
  cdef Color green
  cdef Color blue

Python implementation

cdef class PyColor:
  cdef Color thisobj
  def __cinit__(self, int val):
    self.thisobj = <Color> val

  def get_color_type(self):
    cdef c = {<int>red : "red", <int> green : "green", <int> blue : "blue"}
    return c[<int>self.thisobj]

Answer 2

Here's an alternative solution that uses the ability to change the name of cython and C++ identifiers.

header.hpp

namespace foo {
enum class Bar : uint32_t {
    BAZ,
    QUUX
};
}

header.pxd

cdef extern from "header.hpp" namespace "foo::Bar":
    cdef enum Bar "foo::Bar":
        BAZ,
        QUUX

main.pyx

from header cimport *
cdef void doit(Bar b):
    pass

doit(BAZ) # Not Bar.BAZ, which would have been nicer.

It's effectively telling cython that there exists a namespace called "foo::Bar", and puts a C-style enum in it. To counteract the fact that Bar would otherwise become "foo::Bar::Bar" that is also given an overridden name. It does mean that Bar::BAZ is referred to as BAZ in cython, rather than Bar.BAZ which would be a more idiomatic representation of enum classes, but it seems close enough.