[Python] Replace _have_sundials() with __sundials_version__

Resolves #259.

interfaces/cython/cantera/__init__.py

@@ -1,5 +1,5 @@
 from ._cantera import *
-from ._cantera import __version__, _have_sundials
+from ._cantera import __version__, __sundials_version__
 from .liquidvapor import *
 from .onedim import *
 from .utils import *

interfaces/cython/cantera/test/test_reactor.py

@@ -769,7 +769,7 @@ class TestFlowReactor(utilities.CanteraTest):
             self.assertNear(v0, r.speed)
             self.assertNear(r.distance, v0 * t)
 
-    @unittest.skipUnless(ct._have_sundials(),
+    @unittest.skipUnless(ct.__sundials_version__,
                          "Disabled until there is an interface for setting the "
                          "max_err_test_fails parameter for the old CVODE")
     def test_reacting(self):
@@ -898,7 +898,7 @@ class TestWallKinetics(utilities.CanteraTest):
         self.assertFalse(bool(bad), bad)
 
 
-@unittest.skipUnless(ct._have_sundials(),
+@unittest.skipUnless(ct.__sundials_version__,
                      "Sensitivity calculations require Sundials")
 class TestReactorSensitivities(utilities.CanteraTest):
     def test_sensitivities1(self):

interfaces/cython/cantera/utils.pyx

@@ -26,8 +26,10 @@ def add_directory(directory):
     """ Add a directory to search for Cantera data files. """
     CxxAddDirectory(stringify(directory))
 
-def _have_sundials():
-    return bool(get_sundials_version())
+if get_sundials_version():
+    __sundials_version__ = '.'.join(str(get_sundials_version()))
+else:
+    __sundials_version__ = None
 
 __version__ = pystr(get_cantera_version())