new extend function

1 files changed, 34 insertions, 10 deletions

diff --git a/interface.py b/interface.py
index e94df1b..78f0afa 100644
--- a/interface.py
+++ b/interface.py
@@ -1,4 +1,4 @@
-# Copyright (c) 2000-2004 LOGILAB S.A. (Paris, FRANCE).
+# Copyright (c) 2002-2007 LOGILAB S.A. (Paris, FRANCE).
 # http://www.logilab.fr/ -- mailto:contact@logilab.fr
 #
 # This program is free software; you can redistribute it and/or modify it under
@@ -14,7 +14,7 @@
 # this program; if not, write to the Free Software Foundation, Inc.,
 # 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 """
- bases class for interfaces
+ bases class for interfaces to provide "light" interface handling.
 
  TODO:
   _ implements a check method which check that an object implements the
@@ -31,15 +31,39 @@ class Interface:
     def is_implemented_by(cls, instance):
         return implements(instance, cls)
     is_implemented_by = classmethod(is_implemented_by)
+
     
-def implements(instance, interface):
-    """return true if the instance implements the interface
+def implements(obj, interface):
+    """return true if the give object (maybe an instance or class) implements
+    the interface
     """
-    if hasattr(instance, "__implements__") and \
-           (interface is instance.__implements__ or 
-            (type(instance.__implements__) in (ListType, TupleType) and \
-             interface in instance.__implements__)):
-        return 1
-    return 0
+    kimplements = getattr(obj, '__implements__', ())
+    if not isinstance(kimplements, (list, tuple)):
+        kimplements = (kimplements,)
+    for implementedinterface in kimplements:
+        if issubclass(interface, implementedinterface):
+            return True
+    return False
+
 
+def extend(klass, interface, _recurs=False):
+    """add interface to klass'__implements__ if not already implemented in.
 
+    if klass is subclassed, ensure subclasses __implements__ it as well.
+    
+    NOTE: klass should be e new class.
+    """
+    if not implements(klass, interface):
+        try:
+            kimplements = klass.__implements__
+            kimplementsklass = type(kimplements)
+            kimplements = list(kimplements)
+        except AttributeError:
+            kimplements = []
+        kimplements.append(interface)
+        klass.__implements__ = kimplementsklass(kimplements)
+        for subklass in klass.__subclasses__():
+            extend(subklass, interface, _recurs=True)
+    elif _recurs:
+        for subklass in klass.__subclasses__():
+            extend(subklass, interface, _recurs=True)