Fixed queryset repr mid iteration

Closes #144

docs/changelog.rst

@@ -5,6 +5,7 @@ Changelog
 Changes in dev
 ==============
 
+- Fixed queryet __repr__ mid iteration
 - Added hint() support, so cantell Mongo the proper index to use for the query
 - Fixed issue with inconsitent setting of _cls breaking inherited referencing
 - Added help_text and verbose_name to fields to help with some form libs

mongoengine/queryset.py

@@ -1524,7 +1524,10 @@ class QuerySet(object):
         limit = REPR_OUTPUT_SIZE + 1
         if self._limit is not None and self._limit < limit:
             limit = self._limit
-        data = list(self[self._skip:limit])
+        try:
+            data = list(self[self._skip:limit])
+        except pymongo.errors.InvalidOperation:
+            return ".. queryset mid-iteration .."
         if len(data) > REPR_OUTPUT_SIZE:
             data[-1] = "...(remaining elements truncated)..."
         return repr(data)

tests/queryset.py

@@ -463,6 +463,18 @@ class QuerySetTest(unittest.TestCase):
 
         self.assertEqual(people1, people2)
 
+    def test_repr_iteration(self):
+        """Ensure that QuerySet __repr__ can handle loops
+        """
+        self.Person(name='Person 1').save()
+        self.Person(name='Person 2').save()
+
+        queryset = self.Person.objects
+        self.assertEquals('[<Person: Person object>, <Person: Person object>]', repr(queryset))
+        for person in queryset:
+            self.assertEquals('.. queryset mid-iteration ..', repr(queryset))
+
+
     def test_regex_query_shortcuts(self):
         """Ensure that contains, startswith, endswith, etc work.
         """