--- a/paraspace/structpath.py	Wed Jun 15 01:09:35 2011 +0800
+++ b/paraspace/structpath.py	Wed Jun 15 02:03:38 2011 +0800
@@ -15,6 +15,9 @@
             pass
         self.objs = objs
         pass
+
+    def get_parent(self, obj):
+        raise NotImplementedError, 'get_parent() is not implemented'
     pass
 
 
@@ -46,10 +49,6 @@
     return part == '..'
 
 
-def _get_parent(obj):
-    raise NotImplementedError, '_get_parent() is not implemented'
-
-
 def _obj_attr(obj, attrname):
     if isinstance(obj, list):
         idx = int(attrname)
@@ -62,7 +61,7 @@
 
 def _handle_path_part_obj(ctx, part, obj):
     if _is_parent_name(part):
-        new_objs = [_get_parent(obj)]
+        new_objs = [ctx.get_parent(obj)]
     elif _is_class(part):
         class_name = _class_name(part)
         new_objs = ctx.class_instances[class_name]
@@ -76,19 +75,19 @@
     from itertools import chain
     
     if not ctx.objs:
-        ctx = context([ctx.root], ctx)
+        ctx = ctx.__class__([ctx.root], ctx)
         pass
 
     objss = [_handle_path_part_obj(ctx, part, obj)
              for obj in ctx.objs]
     objs = [o for o in chain(*objss)]
-    new_ctx = context(objs, ctx)
+    new_ctx = ctx.__class__(objs, ctx)
     return new_ctx
 
 
 def _handle_path_parts(ctx, path_parts):
     if _is_abs(path_parts):
-        ctx = context([ctx.root], ctx)
+        ctx = ctx.__class__([ctx.root], ctx)
         path_parts = _rel_of_abs(path_parts)
         pass