Update std::basic_string pythonizations

Author: aaronj0

python/cppyy/__init__.py

@@ -125,14 +125,18 @@ def tuple_getitem(self, idx, get=cppyy.gbl.std.get):
             raise IndexError(idx)
         pyclass.__getitem__ = tuple_getitem
 
-  # pythoniztion of std::string; placed here because it's simpler to write the
+  # pythonization of std::basic_string<char>; placed here because it's simpler to write the
   # custom "npos" object (to allow easy result checking of find/rfind) in Python
     elif pyclass.__cpp_name__ == "std::basic_string<char>":
-        class NPOS(0x3000000 <= sys.hexversion and int or long):
+        class NPOS(int):
+            def __init__(self, npos):
+                self.__cpp_npos = npos
             def __eq__(self, other):
-                return other == -1 or  int(self) == other
+                return other == -1 or  other == self.__cpp_npos
             def __ne__(self, other):
-                return other != -1 and int(self) != other
+                return other != -1 and other != self.__cpp_npos
+        if hasattr(pyclass.__class__, 'npos'):
+            del pyclass.__class__.npos          # drop b/c is const data
         pyclass.npos = NPOS(pyclass.npos)
 
     return True