diff --git a/mercurial/demandload.py b/mercurial/demandload.py
new file mode 100644
--- /dev/null
+++ b/mercurial/demandload.py
@@ -0,0 +1,15 @@
+def demandload(scope, modules):
+    class d:
+        def __getattr__(self, name):
+            mod = self.__dict__["mod"]
+            scope = self.__dict__["scope"]
+            scope[mod] = __import__(mod, scope, scope, [])
+            return getattr(scope[mod], name)
+
+    for m in modules.split():
+        dl = d()
+        dl.mod = m
+        dl.scope = scope
+        scope[m] = dl
+
+