--- a/cubicweb/schema.py	Wed Jan 24 12:03:21 2018 +0100
+++ b/cubicweb/schema.py	Fri Jan 12 10:17:10 2018 +0100
@@ -19,6 +19,7 @@
 
 from __future__ import print_function
 
+from functools import wraps
 import re
 from os.path import join
 from hashlib import md5
@@ -594,8 +595,28 @@
         return text_type(req._(key))
 
 
+def _override_method(cls, method_name=None, pass_original=False):
+    """Override (or set) a method on `cls`."""
+    def decorator(func):
+        name = method_name or func.__name__
+        orig = None
+        if pass_original:
+            orig = getattr(cls, name)
+
+        @wraps(func)
+        def wrapper(*args, **kwargs):
+            if orig is not None:
+                kwargs['_orig'] = orig
+            return func(*args, **kwargs)
+
+        setattr(cls, name, wrapper)
+
+    return decorator
+
+
 # Schema objects definition ###################################################
 
+@_override_method(ERSchema, 'display_name')
 def ERSchema_display_name(self, req, form='', context=None):
     """return a internationalized string for the entity/relation type name in
     a given form
@@ -603,9 +624,7 @@
     return display_name(req, self.type, form, context)
 
 
-ERSchema.display_name = ERSchema_display_name
-
-
+@_override_method(PermissionMixIn)
 @cached
 def get_groups(self, action):
     """return the groups authorized to perform <action> on entities of
@@ -624,9 +643,7 @@
         return ()
 
 
-PermissionMixIn.get_groups = get_groups
-
-
+@_override_method(PermissionMixIn)
 @cached
 def get_rqlexprs(self, action):
     """return the rql expressions representing queries to check the user is allowed
@@ -645,10 +662,8 @@
         return ()
 
 
-PermissionMixIn.get_rqlexprs = get_rqlexprs
-
-
-def set_action_permissions(self, action, permissions):
+@_override_method(PermissionMixIn, pass_original=True)
+def set_action_permissions(self, action, permissions, _orig):
     """set the groups and rql expressions allowing to perform <action> on
     entities of this type
 
@@ -658,15 +673,12 @@
     :type permissions: tuple
     :param permissions: the groups and rql expressions allowing the given action
     """
-    orig_set_action_permissions(self, action, tuple(permissions))
+    _orig(self, action, tuple(permissions))
     clear_cache(self, 'get_rqlexprs')
     clear_cache(self, 'get_groups')
 
 
-orig_set_action_permissions = PermissionMixIn.set_action_permissions
-PermissionMixIn.set_action_permissions = set_action_permissions
-
-
+@_override_method(PermissionMixIn)
 def has_local_role(self, action):
     """return true if the action *may* be granted locally (i.e. either rql
     expressions or the owners group are used in security definition)
@@ -682,9 +694,7 @@
     return False
 
 
-PermissionMixIn.has_local_role = has_local_role
-
-
+@_override_method(PermissionMixIn)
 def may_have_permission(self, action, req):
     if action != 'read' and not (self.has_local_role('read') or
                                  self.has_perm(req, 'read')):
@@ -692,9 +702,7 @@
     return self.has_local_role(action) or self.has_perm(req, action)
 
 
-PermissionMixIn.may_have_permission = may_have_permission
-
-
+@_override_method(PermissionMixIn)
 def has_perm(self, _cw, action, **kwargs):
     """return true if the action is granted globally or locally"""
     try:
@@ -704,9 +712,7 @@
         return False
 
 
-PermissionMixIn.has_perm = has_perm
-
-
+@_override_method(PermissionMixIn)
 def check_perm(self, _cw, action, **kwargs):
     # NB: _cw may be a server transaction or a request object.
     #
@@ -749,9 +755,6 @@
     raise Unauthorized(action, str(self))
 
 
-PermissionMixIn.check_perm = check_perm
-
-
 CubicWebRelationDefinitionSchema._RPROPERTIES['eid'] = None
 # remember rproperties defined at this point. Others will have to be serialized in
 # CWAttribute.extra_props
@@ -1464,33 +1467,23 @@
 
 # XXX itou for some Statement methods
 
-def bw_get_etype(self, name):
-    return orig_get_etype(self, bw_normalize_etype(name))
-
-
-orig_get_etype = stmts.ScopeNode.get_etype
-stmts.ScopeNode.get_etype = bw_get_etype
-
-
-def bw_add_main_variable_delete(self, etype, vref):
-    return orig_add_main_variable_delete(self, bw_normalize_etype(etype), vref)
+@_override_method(stmts.ScopeNode, pass_original=True)
+def get_etype(self, name, _orig):
+    return _orig(self, bw_normalize_etype(name))
 
 
-orig_add_main_variable_delete = stmts.Delete.add_main_variable
-stmts.Delete.add_main_variable = bw_add_main_variable_delete
-
-
-def bw_add_main_variable_insert(self, etype, vref):
-    return orig_add_main_variable_insert(self, bw_normalize_etype(etype), vref)
+@_override_method(stmts.Delete, method_name='add_main_variable',
+                  pass_original=True)
+def _add_main_variable_delete(self, etype, vref, _orig):
+    return _orig(self, bw_normalize_etype(etype), vref)
 
 
-orig_add_main_variable_insert = stmts.Insert.add_main_variable
-stmts.Insert.add_main_variable = bw_add_main_variable_insert
+@_override_method(stmts.Insert, method_name='add_main_variable',
+                  pass_original=True)
+def _add_main_variable_insert(self, etype, vref, _orig):
+    return _orig(self, bw_normalize_etype(etype), vref)
 
 
-def bw_set_statement_type(self, etype):
-    return orig_set_statement_type(self, bw_normalize_etype(etype))
-
-
-orig_set_statement_type = stmts.Select.set_statement_type
-stmts.Select.set_statement_type = bw_set_statement_type
+@_override_method(stmts.Select, pass_original=True)
+def set_statement_type(self, etype, _orig):
+    return _orig(self, bw_normalize_etype(etype))