Added check for Python 2 or Python 3

__init__.py

@@ -1,7 +1,4 @@
 
-
-
-
 #    pyeq3 is a collection of equations expressed as Python classes
 #
 #    Copyright (C) 2013 James R. Phillips
@@ -12,6 +9,11 @@
 #
 #    License: BSD-style (see LICENSE.txt in main source directory)
 
+import sys
+ver = sys.version_info[0]
+if ver < 3:
+    raise Exception('Python 3 is required to use pyeq3')
+
 from . import DataCache
 from . import Services
 from . import ExtendedVersionHandlers
@@ -22,4 +24,4 @@
 dataConvertorService = Services.DataConverterService.DataConverterService
 solverService = Services.SolverService.SolverService
 outputSourceCodeService = Services.OutputSourceCodeService.OutputSourceCodeService
-dataCache = DataCache.DataCache.DataCache
+dataCache = DataCache.DataCache.DataCache