Add clear comment and tests for positional push #1565

mongoengine/queryset/transform.py

@@ -336,10 +336,11 @@ def update(_doc_cls=None, **update):
         elif op == 'addToSet' and isinstance(value, list):
             value = {key: {'$each': value}}
         elif op == 'push':
-            if parts[-1].isdigit() and op == 'push':
+            if parts[-1].isdigit():
                 key = parts[0]
                 position = int(parts[-1])
-                # position modifier must appear with each.
+                # $position expects an iterable. If pushing a single value,
+                # wrap it in a list.
                 if not isinstance(value, (set, tuple, list)):
                     value = [value]
                 value = {key: {'$each': value, '$position': position}}