Random objects should not be affected by list/dict modifications

jedi/inference/base_value.py

@@ -140,9 +140,12 @@ class HelperValueMixin(object):
 
 class Value(HelperValueMixin, BaseValue):
     """
-    To be defined by subclasses.
+    To be implemented by subclasses.
     """
     tree_node = None
+    # Possible values: None, tuple, list, dict and set. Here to deal with these
+    # very important containers.
+    array_type = None
 
     @property
     def api_type(self):

test/completion/dynamic_arrays.py

@@ -327,7 +327,7 @@ some_lst[0]
 some_lst[1]
 
 # -----------------
-# set setitem (should not work)
+# set setitem/other modifications (should not work)
 # -----------------
 
 some_set = {int}
@@ -337,6 +337,13 @@ some_set[0]
 #? int
 some_set[3]
 
+something = object()
+something[3] = str
+#? 
+something[0]
+#?
+something[3]
+
 # -----------------
 # dict setitem
 # -----------------