better errors in custom_import, thanks Michele

VERSION

@@ -1 +1 @@
-Version 2.1.0 (2012-10-15 05:33:14) dev
+Version 2.1.0 (2012-10-15 05:46:52) dev

gluon/custom_import.py

@@ -11,10 +11,12 @@ from gluon import current
 
 NATIVE_IMPORTER = __builtin__.__import__
 TRACK_CHANGES = False
-INVALID_MODULES = set(sys.modules.keys()).union(('','gluon','applications','custom_import'))
+INVALID_MODULES = set(('','gluon','applications','custom_import'))
 
 # backward compatibility API
 def custom_import_install():
+    if __builtin__.__import__ != custom_importer:
+        INVALID_MODULES = INVALID_MODULES.union(sys.modules.keys())
         __builtin__.__import__ = custom_importer
 
 def track_changes(track=True):
@@ -25,6 +27,9 @@ def track_changes(track=True):
 def is_tracking_changes():
     return TRACK_CHANGES
 
+class CustomImportException(ImportError):
+    pass
+
 def custom_importer(name, globals=None, locals=None, fromlist=None, level=-1):
     """
     The web2py custom importer. Like the standard Python importer but it
@@ -44,6 +49,7 @@ def custom_importer(name, globals=None, locals=None, fromlist=None, level=-1):
             and level<=0 \
             and not name.split('.')[0] in INVALID_MODULES \
             and isinstance(globals, dict):
+        import_tb = None
         try:
             items = current.request.folder.split(os.path.sep)
             if not items[-1]: items = items[:-1]
@@ -65,9 +71,17 @@ def custom_importer(name, globals=None, locals=None, fromlist=None, level=-1):
                 pname = modules_prefix + "." + name
                 return base_importer(pname, globals, locals, fromlist, level)
         except ImportError, e1:
-            pass # the module does not exist
+            import_tb = sys.exc_info()[2]
+            try:
+                return NATIVE_IMPORTER(name,globals,locals,fromlist,level)
+            except ImportError, e3:
+                raise ImportError, e1, import_tb # there an import error in the module
         except Exception, e2:
             raise e2 # there is an error in the module
+        finally:
+            if import_tb:
+                import_tb = None
+
     return NATIVE_IMPORTER(name,globals,locals,fromlist,level)