Use clearer input syntax for hexagonal lattice pitch

armi/reactor/blueprints/gridBlueprint.py

@@ -130,6 +130,50 @@ def __init__(self, x=0.0, y=0.0, z=0.0):
         self.z = z
 
 
+class Pitch(yamlize.Object):
+    """A x, y, z triplet or triangular hex pitch for coordinates or lattice pitch."""
+
+    hex = yamlize.Attribute(type=float, default=0.0)
+    x = yamlize.Attribute(type=float, default=0.0)
+    y = yamlize.Attribute(type=float, default=0.0)
+    z = yamlize.Attribute(type=float, default=0.0)
+
+    def __init__(self, hex=0.0, x=0.0, y=0.0, z=0.0):
+        """
+        Parameters
+        ----------
+        hex : float, optional
+            Triangular/hex lattice pitch
+        x : float, optional
+            Cartesian grid: pitch in the x direction
+            Hexagonal grid: interpreted as hex lattice pitch
+        y : float, optional
+            Cartesian grid: pitch in the y direction
+        z : float, optional
+            Pitch in the z direction
+
+        Raises
+        ------
+        InputError
+            * If a `hex` pitch and `x` or `y` pitch are provided simultaneously.
+            * If no non-zero value is provided for any parameter.
+        """
+        if hex and (x or y):
+            raise InputError(
+                "Cannot mix `hex` with `x` and `y` attributes of `latticePitch`."
+            )
+
+        if not any(hex, x, y, z):
+            raise InputError(
+                "`lattice pitch` must have at least one non-zero attribute! Check the blueprints."
+            )
+
+        self.hex = hex or x
+        self.x = x
+        self.y = y
+        self.z = z
+
+
 class GridBlueprint(yamlize.Object):
     """
     A grid input blueprint.
@@ -169,9 +213,9 @@ class GridBlueprint(yamlize.Object):
         The geometry of the grid (e.g. 'cartesian')
     latticeMap : str
         An asciimap representation of the lattice contents
-    latticeDimensions : Triplet
-        An x/y/z Triplet with grid dimensions in cm. This is used to specify a uniform grid, such as
-        Cartesian or Hex. Mutually exclusive with gridBounds.
+    latticeDimensions : Pitch
+        An x/y/z Triplet or hex pitch with grid dimensions in cm. This is used to specify a
+        uniform grid, such as Cartesian or Hex. Mutually exclusive with gridBounds.
     gridBounds : dict
         A dictionary containing explicit grid boundaries. Specific keys used will depend on the type
         of grid being defined. Mutually exclusive with latticeDimensions.
@@ -185,9 +229,7 @@ class GridBlueprint(yamlize.Object):
     name = yamlize.Attribute(key="name", type=str)
     geom = yamlize.Attribute(key="geom", type=str, default=geometry.HEX)
     latticeMap = yamlize.Attribute(key="lattice map", type=str, default=None)
-    latticeDimensions = yamlize.Attribute(
-        key="lattice pitch", type=Triplet, default=None
-    )
+    latticeDimensions = yamlize.Attribute(key="lattice pitch", type=Pitch, default=None)
     gridBounds = yamlize.Attribute(key="grid bounds", type=dict, default=None)
     symmetry = yamlize.Attribute(
         key="symmetry",
@@ -306,7 +348,21 @@ def _constructSpatialGrid(self):
                     )
             spatialGrid = grids.ThetaRZGrid(bounds=(theta, radii, (0.0, 0.0)))
         if geom in (geometry.HEX, geometry.HEX_CORNERS_UP):
-            pitch = self.latticeDimensions.x if self.latticeDimensions else 1.0
+            if not self.latticeDimensions:
+                pitch = 1.0
+            else:
+                ld = self.latticeDimensions
+                if ld.hex and (ld.x or ld.y):
+                    raise InputError(
+                        "Cannot mix `hex` with `x` and `y` attributes of `latticePitch`."
+                    )
+
+                if not any([ld.hex, ld.x, ld.y, ld.z]):
+                    raise InputError(
+                        "`lattice pitch` must have at least one non-zero attribute! Check the blueprints."
+                    )
+
+                pitch = ld.hex or ld.x
             # add 2 for potential dummy assems
             spatialGrid = grids.HexGrid.fromPitch(
                 pitch,

armi/reactor/blueprints/tests/test_gridBlueprints.py

@@ -30,6 +30,7 @@
 control:
     geom: hex_corners_up
     symmetry: full
+    lattice pitch: {{hex: 1.2}}
     lattice map: |
        - - - - - - - - - 1 1 1 1 1 1 1 1 1 4
         - - - - - - - - 1 1 1 1 1 1 1 1 1 1 1
@@ -360,7 +361,8 @@ def tearDown(self):
 
     def test_simpleRead(self):
         gridDesign = self.grids["control"]
-        _ = gridDesign.construct()
+        grid = gridDesign.construct()
+        self.assertAlmostEqual(grid.pitch, 1.2)
         self.assertEqual(gridDesign.gridContents[-8, 0], "6")
 
         # Cartesian full, odd