improved cython wrapper python3 support

cmake/FindCython.cmake

@@ -32,7 +32,7 @@
 find_package( PythonInterp )
 if ( PYTHONINTERP_FOUND )
   execute_process( COMMAND "${PYTHON_EXECUTABLE}" "-c"
-      "import Cython; print Cython.__path__"
+      "import Cython; print(Cython.__path__[0])"
       RESULT_VARIABLE RESULT
       OUTPUT_VARIABLE CYTHON_PATH
       OUTPUT_STRIP_TRAILING_WHITESPACE
@@ -51,7 +51,7 @@ endif ()
 # RESULT=0 means ok
 if ( NOT RESULT )
   execute_process( COMMAND "${PYTHON_EXECUTABLE}" "-c"
-      "import Cython; print Cython.__version__"
+      "import Cython; print(Cython.__version__)"
       RESULT_VARIABLE RESULT
       OUTPUT_VARIABLE CYTHON_VAR_OUTPUT
       ERROR_VARIABLE CYTHON_VAR_OUTPUT

cython/gtsam/__init__.py.in

@@ -1,2 +1,2 @@
-from gtsam import *
+from .gtsam import *
 ${GTSAM_UNSTABLE_IMPORT}

wrap/Module.cpp

@@ -394,6 +394,10 @@ void Module::emit_cython_pxd(FileWriter& pxdFile) const {
 
 /* ************************************************************************* */
 void Module::emit_cython_pyx(FileWriter& pyxFile) const {
+  // directives...
+  // allow str to automatically coerce to std::string and back (for python3)
+  pyxFile.oss << "# cython: c_string_type=str, c_string_encoding=ascii\n\n";
+
   // headers...
   string pxdHeader = name;
   pyxFile.oss << "cimport numpy as np\n"

wrap/tests/expected-cython/geometry.pyx

@@ -1,3 +1,5 @@
+# cython: c_string_type=str, c_string_encoding=ascii
+
 cimport numpy as np
 import numpy as npp
 cimport geometry