Merge pull request ipython#430 from ankostis/fix_emptystr_listopopts

Fix parsing of deprecated list options failing with empty strings

Author: minrk

traitlets/config/loader.py

@@ -543,7 +543,7 @@ def _exec_config_str(self, lhs, rhs, trait=None):
 
         elif isinstance(rhs, (list, tuple)):
             value = None
-            if len(rhs) == 1:
+            if len(rhs) == 1 and len(rhs[0]) > 0:
                 # check for deprecated --Class.trait="['a', 'b', 'c']"
                 r = rhs[0]
                 if (

traitlets/config/tests/test_loader.py

@@ -345,6 +345,13 @@ def test_seq_traits(self):
         self.assertEqual(config.CSub.d, [1, 'BBB'])
         self.assertEqual(config.CSub.e, [1, 'a', 'bcd'])
 
+    def test_seq_traits_single_empty_string(self):
+        cl = self.klass(log=log, classes=(CBase, ))
+        aliases = {'seqopt': 'CBase.c'}
+        argv = ['--seqopt', '']
+        config = cl.load_config(argv, aliases=aliases)
+        self.assertEqual(config.CBase.c, [''])
+
     def test_dict_traits(self):
         cl = self.klass(log=log, classes=(CBase, CSub))
         aliases = {'D': 'CBase.adict', 'E': 'CSub.bdict'}