Fix contextualizing of subscriptlist

jedi/inference/syntax_tree.py

@@ -406,7 +406,7 @@ def _infer_expr_stmt(context, stmt, seek_name=None):
 
         if is_setitem:
             def to_mod(v):
-                c = ContextualizedNode(context, subscriptlist)
+                c = ContextualizedSubscriptListNode(context, subscriptlist)
                 if v.array_type == 'dict':
                     return DictModification(v, value_set, c)
                 elif v.array_type == 'list':
@@ -803,6 +803,11 @@ def check_tuple_assignments(name, value_set):
     return value_set
 
 
+class ContextualizedSubscriptListNode(ContextualizedNode):
+    def infer(self):
+        return _infer_subscript_list(self.context, self.node)
+
+
 def _infer_subscript_list(context, index):
     """
     Handles slices in subscript nodes.

test/completion/dynamic_arrays.py

@@ -335,6 +335,11 @@ some_lst2[3]
 #? int() str()
 some_lst2[2]
 
+some_lst3 = []
+some_lst3[0] = 3
+some_lst3[:] = ''  # Is ignored for now.
+#? int()
+some_lst3[0]
 # -----------------
 # set setitem/other modifications (should not work)
 # -----------------