Add two features requested in the review of PR185

src/tdastro/graph_state.py

@@ -58,6 +58,17 @@ def __init__(self, num_samples=1):
     def __len__(self):
         return self.num_parameters
 
+    def __next__(self):
+        return next(self._iterate())
+
+    def __iter__(self):
+        return self._iterate()
+
+    def _iterate(self):
+        """Returns a single sliced state."""
+        for idx in range(self.num_samples):
+            yield self.extract_single_sample(idx)
+
     def __contains__(self, key):
         if key in self.states:
             return True
@@ -66,6 +77,11 @@ def __contains__(self, key):
             if len(tokens) != 2:
                 raise KeyError(f"Invalid GraphState key: {key}")
             return tokens[0] in self.states and tokens[1] in self.states[tokens[0]]
+        elif len(self.states) == 1:
+            # Special case when we have only a single node stored in the graph state.
+            node_state = list(self.states.values())[0]
+            if key in node_state:
+                return True
         else:
             return False
 
@@ -115,6 +131,12 @@ def __getitem__(self, key):
             if len(tokens) != 2:
                 raise KeyError(f"Invalid GraphState key: {key}")
             return self.states[tokens[0]][tokens[1]]
+        elif len(self.states) == 1:
+            # Special case when we have only a single node stored
+            # in the graph state.
+            node_state = list(self.states.values())[0]
+            if key in node_state:
+                return node_state[key]
         else:
             raise KeyError(f"Unknown GraphState key: {key}")
 

tests/tdastro/test_graph_state.py

@@ -40,6 +40,18 @@ def test_create_single_sample_graph_state():
     assert a_vals["v1"] == 1.0
     assert a_vals["v2"] == 2.0
 
+    # If the state only has a single node, we can access that node's variables
+    # directly. But we get an error if we try to do this with multiple nodes.
+    state2 = GraphState()
+    state2.set("a", "v1", 1.0)
+    state2.set("a", "v2", 2.0)
+    assert state2["v1"] == 1.0
+    assert state2["v2"] == 2.0
+
+    state2.set("b", "v3", 3.0)
+    with pytest.raises(KeyError):
+        _ = state["v1"]
+
     # Can't access an out-of-bounds sample_num.
     with pytest.raises(ValueError):
         _ = state.get_node_state("a", 2)
@@ -91,6 +103,14 @@ def test_graph_state_contains():
     with pytest.raises(KeyError):
         assert "b.v1.v2" not in state
 
+    # If the state only has a single node, we can access that node's variables directly.
+    state2 = GraphState()
+    state2.set("a", "v1", 1.0)
+    state2.set("a", "v2", 2.0)
+    assert "a" in state2
+    assert "v1" in state2
+    assert "v2" in state2
+
 
 def test_create_multi_sample_graph_state():
     """Test that we can create and access a multi-sample GraphState."""
@@ -158,6 +178,23 @@ def test_create_multi_sample_graph_state_reference():
     assert np.allclose(state2["b"]["v1"], [2.0, 2.5, 3.0, 3.5, 4.0])
 
 
+def test_graph_state_iterate():
+    """Test that we can use an iterator to transform a GraphState with
+    multiple samples into a list of GraphStates each with a single sample.
+    """
+    state = GraphState(10)
+    state.set("a", "v1", 1.0)
+    state.set("a", "v2", np.arange(10))
+
+    list_version = [x for x in state]
+    assert len(list_version) == 10
+    for i in range(10):
+        sample_state = list_version[i]
+        assert sample_state.num_samples == 1
+        assert sample_state["a.v1"] == 1.0
+        assert sample_state["a.v2"] == i
+
+
 def test_graph_state_equal():
     """Test that we use == on GraphStates."""
     state1 = GraphState(num_samples=2)