Fix action selection key iteration.

It was failing without a named action.

CHANGES.rst

@@ -98,7 +98,9 @@ Release History
   ``prob_cleanup``. Also, fix the function's incorrect documentation.
   (`#203 <https://github.com/nengo/nengo_spa/issues/203>`__,
   `#206 <https://github.com/nengo/nengo_spa/pull/206>`__)
-
+- Fix ``nengo_spa.ActionSelection.keys()`` when no named actions have been
+  provided.
+  (`#210 <https://github.com/nengo/nengo_spa/pull/210>`_)
 
 
 0.5.2 (July 6, 2018)

nengo_spa/action_selection.py

@@ -135,6 +135,7 @@ def __getitem__(self, key):
     def __iter__(self):
         # Given not all actions have names, there will actions whose keys
         # will be numbers and not names.
+        i = -1
         for i, (name, v) in enumerate(self._name2idx.items()):
             while i < v:
                 yield i

nengo_spa/tests/test_action_selection.py

@@ -378,3 +378,15 @@ def test_naming_of_actions():
     assert action_sel['name2'] is u2
     for i, u in enumerate((u0, u1, u2)):
         assert action_sel[i] is u
+
+
+def test_action_selection_keys_corner_cases():
+    with spa.Network():
+        with ActionSelection() as action_sel:
+            pass
+    assert list(action_sel.keys()) == []
+
+    with spa.Network():
+        with ActionSelection() as action_sel:
+            spa.ifmax(0.)
+    assert list(action_sel.keys()) == [0]