PySquare.pyx

# distutils: language = c++
# distutils: sources = squaremod.cpp

# call to the c++ header, `except +` allows a python error to
# be raised in the case there is an allocation error
# includes the variable and call to the method inc. what kind of variable you are passing it
cdef extern from "squaremod.h" namespace "ops":
    cdef cppclass Powers:
        Powers() except +
        double x
        double getSqr(double)
        double getCube(double)


# call the inctance of the c class
cdef class PySquare:     
    cdef Powers c_powers # hold a C++ instance of what you're wrapping

    # initialise the C class    
    def __cinit__(self):
        self.c_powers = Powers()

    # actually call the function we're wanting
    def get_sqr(self, double x):
        return self.c_powers.getSqr(x)
	
    # call another function from the class
    def get_cube(self, double x):
        return self.c_powers.getCube(x)

setup.py

from distutils.core import setup
from Cython.Build import cythonize

ext_modules=cythonize(
              "PySquare.pyx",
              sources=['squaremod.cpp'],
              language="c++",
          )

setup(
    name = "squaremod",
    ext_modules = ext_modules
)

squaremod.cpp

#include "squaremod.h"

namespace ops {
  Powers :: Powers() {}
    
    Powers::~Powers() {}
            
    double Powers::getSqr(double x) {
      return x*x;
    }
    double Powers::getCube(double x) {
      return x*x*x;
    }	
}

squaremod.h

namespace ops {
	class Powers{
	public:
	  double x;
	  Powers();
	  ~Powers();
	  double getSqr(double x);
	  double getCube(double x);
	};
}