diff --git a/patacrep/utils.py b/patacrep/utils.py
new file mode 100644
index 00000000..f61b447d
--- /dev/null
+++ b/patacrep/utils.py
@@ -0,0 +1,51 @@
+from collections import UserDict
+
+class DictOfDict(UserDict):
+    """Dictionary, with a smart :meth:`update` method.
+
+    By "smart", we mean: if `self.update(other)` is called, and for some key
+    both `self[key]` and `other[key]` are dictionary, then `self[key]` is not
+    replaced by `other[key]`, but instead is updated.
+
+    >>> ordinal = DictOfDict({
+    ... "francais": {
+    ...     1: "premier",
+    ...     2: "deuxieme",
+    ...     },
+    ... "english": {
+    ...     1: "first",
+    ...     },
+    ... })
+    >>> ordinal.update({
+    ... "francais": {
+    ...     2: "second",
+    ...     3: "troisieme",
+    ...     },
+    ... "espanol": {
+    ...     1: "primero",
+    ...     },
+    ... })
+    >>> ordinal == {
+    ...     "francais": {
+    ...         1: "premier",
+    ...         2: "second",
+    ...         3: "troisieme",
+    ...         },
+    ...     "english": {
+    ...         1: "first",
+    ...         },
+    ...     "espanol": {
+    ...         1: "primero",
+    ...         },
+    ...     }
+    True
+    """
+
+    def update(self, other):
+        for key in other:
+            if key not in self:
+                self[key] = other[key]
+            elif isinstance(self[key], dict) and isinstance(other[key], dict):
+                self[key].update(other[key])
+            else:
+                self[key] = other[key]