Small refactor to make _isdupitem more DRY.

bidict/_base.py

@@ -298,16 +298,20 @@ def _dedup_item(self, key, val, on_dup):
         # else neither isdupkey nor isdupval.
         return dedup_result
 
-    @staticmethod
-    def _isdupitem(key, val, dedup_result):
-        isdupkey, isdupval, oldkey, oldval = dedup_result
-        isdupitem = oldkey == key
-        assert isdupitem == (oldval == val), '%r %r %r' % (key, val, dedup_result)
+    def _isdupitem(self, key, val, dedup_result):
+        """Return whether (key, val) duplicates an existing item."""
+        isdupkey, isdupval, invbyval, fwdbykey = dedup_result
+        isdupitem = self._isdupitem_helper(key, val, invbyval, fwdbykey)
         if isdupitem:
             assert isdupkey
             assert isdupval
         return isdupitem
 
+    def _isdupitem_helper(self, key, val, oldkey, oldval):  # pylint: disable=no-self-use
+        isdupitem = oldkey == key
+        assert isdupitem == (oldval == val), '%r %r %r %r' % (key, val, oldkey, oldval)
+        return isdupitem
+
     @classmethod
     def _get_on_dup(cls, on_dup=None):
         if on_dup is None:

bidict/_orderedbase.py

@@ -198,13 +198,8 @@ def _pop(self, key):
         nodefwd.nxt.prv = nodefwd.prv
         return val
 
-    def _isdupitem(self, key, val, dedup_result):
-        """Return whether (key, val) duplicates an existing item."""
-        isdupkey, isdupval, nodeinv, nodefwd = dedup_result
+    def _isdupitem_helper(self, key, val, nodeinv, nodefwd):  # pylint: disable=arguments-differ
         isdupitem = nodeinv is nodefwd
-        if isdupitem:
-            assert isdupkey
-            assert isdupval
         return isdupitem
 
     def _write_item(self, key, val, dedup_result):  # pylint: disable=too-many-locals