Cython: How to export C++ class to .hpp header instead of C .h header

user_5581893 0
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This works fine in .pxd file:

cdef public:
    struct foo:
        float bar

But this doesn't work:

cdef public:
    class foo:
        float bar # Syntax error in simple statement list

This works but Cython is still making struct instead of class and the resulting file is .h file instead of .hpp (or .hh) file:

cdef public:
    cppclass foo:
        float bar

My file is called mod.pyx and Cython transpiles the cppclass right above as:

#ifndef __PYX_HAVE__mod
#define __PYX_HAVE__mod

#include "Python.h"
struct foo;
struct foo {

  /* "mod.pyx":21
 *
 * cdef public:
 *     cppclass foo:             # <<<<<<<<<<<<<<
 *         float bar
 *
 */
  float bar;
};

How to make real C++ output from Cython transpilation? I mean .hpp or .hh files with class keyword inside. It's possible to use a separate C++ header file instead but I would like to make the source code fully Cython.

The transpile command is:
cython3 -3 --cplus --fast-fail mod.pyx

transpiler cython header python c++
1 Answers

I've figured out how to define C++ class (not the Python extension type 'class') in Cython only; it is still transpiled to .h file as struct but with methods inside:

# Declaration
cdef public:
    cppclass foo:
        float bar
        foo() # Constructor
        method() # Sample method

# Implementation
cdef cppclass foo:
    method():
        cdef foo* p = this # 'this' can be used
        print(p.bar+1) # Test

There are some notes:

  • The nullary constructor is a must, Cython says so
    • This doesn't require constructor: cdef foo* f = new foo()
    • This requires a constructor: cdef foo f = foo()
      • Or error: no constructor found for C++ type 'foo'
  • No overloads in Python, which applies to Cython and so no constructor overloads (?); properties to be set by a method instead
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