clarify and test tgt_location defaults

esmf_regrid/experimental/unstructured_scheme.py

@@ -326,7 +326,7 @@ def __init__(
             a boolean value. If True, this array is taken from the mask on the data
             in ``tgt``. If False, no mask will be taken and all points
             will be used in weights calculation.
-        tgt_location : str or None, default="face"
+        tgt_location : str or None, default=None
             Either "face" or "node". Describes the location for data on the mesh
             if the target is not a :class:`~iris.cube.Cube`.
 

esmf_regrid/schemes.py

@@ -849,7 +849,7 @@ class ESMFAreaWeighted:
     """
 
     def __init__(
-        self, mdtol=0, use_src_mask=False, use_tgt_mask=False, tgt_location=None
+        self, mdtol=0, use_src_mask=False, use_tgt_mask=False, tgt_location="face"
     ):
         """
         Area-weighted scheme for regridding between rectilinear grids.
@@ -870,18 +870,22 @@ def __init__(
         use_tgt_mask : bool, default=False
             If True, derive a mask from target cube which will tell :mod:`esmpy`
             which points to ignore.
-        tgt_location : str or None, default=None
+        tgt_location : str or None, default="face"
             Either "face" or "node". Describes the location for data on the mesh
             if the target is not a :class:`~iris.cube.Cube`.
 
         """
         if not (0 <= mdtol <= 1):
             msg = "Value for mdtol must be in range 0 - 1, got {}."
             raise ValueError(msg.format(mdtol))
+        if tgt_location is not None and tgt_location != "face":
+            raise ValueError(
+                "For area weighted regridding, target location must be 'face'."
+            )
         self.mdtol = mdtol
         self.use_src_mask = use_src_mask
         self.use_tgt_mask = use_tgt_mask
-        self.tgt_location = tgt_location
+        self.tgt_location = "face"
 
     def __repr__(self):
         """Return a representation of the class."""
@@ -893,7 +897,7 @@ def regridder(
         tgt_grid,
         use_src_mask=None,
         use_tgt_mask=None,
-        tgt_location=None,
+        tgt_location="face",
     ):
         """
         Create regridder to perform regridding from ``src_grid`` to ``tgt_grid``.
@@ -911,7 +915,7 @@ def regridder(
         use_tgt_mask : :obj:`~numpy.typing.ArrayLike` or bool, optional
             Array describing which elements :mod:`esmpy` will ignore on the tgt_grid.
             If True, the mask will be derived from tgt_grid.
-        tgt_location : str or None, default=None
+        tgt_location : str or None, default="face"
             Either "face" or "node". Describes the location for data on the mesh
             if the target is not a :class:`~iris.cube.Cube`.
 
@@ -934,15 +938,17 @@ def regridder(
             use_src_mask = self.use_src_mask
         if use_tgt_mask is None:
             use_tgt_mask = self.use_tgt_mask
-        if tgt_location is None:
-            tgt_location = self.tgt_location
+        if tgt_location is not None and tgt_location != "face":
+            raise ValueError(
+                "For area weighted regridding, target location must be 'face'."
+            )
         return ESMFAreaWeightedRegridder(
             src_grid,
             tgt_grid,
             mdtol=self.mdtol,
             use_src_mask=use_src_mask,
             use_tgt_mask=use_tgt_mask,
-            tgt_location=tgt_location,
+            tgt_location="face",
         )
 
 

esmf_regrid/tests/unit/schemes/test_ESMFAreaWeighted.py

@@ -51,3 +51,14 @@ def test_mask_from_regridder(mask_keyword):
     Checks that use_src_mask and use_tgt_mask are passed down correctly.
     """
     _test_mask_from_regridder(ESMFAreaWeighted, mask_keyword)
+
+
+def test_invalid_tgt_location():
+    """
+    Test initialisation of :class:`esmf_regrid.schemes.ESMFAreaWeighted`.
+
+    Checks that initialisation fails when tgt_location is not "face".
+    """
+    match = "For area weighted regridding, target location must be 'face'."
+    with pytest.raises(ValueError, match=match):
+        _ = ESMFAreaWeighted(tgt_location="node")

esmf_regrid/tests/unit/schemes/test_ESMFAreaWeightedRegridder.py

@@ -88,6 +88,24 @@ def test_invalid_mdtol():
         _ = ESMFAreaWeightedRegridder(src, tgt, mdtol=-1)
 
 
+def test_invalid_tgt_location():
+    """
+    Test initialisation of :class:`esmf_regrid.schemes.ESMFAreaWeightedRegridder`.
+
+    Checks that initialisation fails when tgt_location is not "face".
+    """
+    n_lons = 6
+    n_lats = 5
+    lon_bounds = (-180, 180)
+    lat_bounds = (-90, 90)
+    src = _grid_cube(n_lons, n_lats, lon_bounds, lat_bounds, circular=True)
+    tgt = _grid_cube(n_lons, n_lats, lon_bounds, lat_bounds, circular=True)
+
+    match = "For area weighted regridding, target location must be 'face'."
+    with pytest.raises(ValueError, match=match):
+        _ = ESMFAreaWeightedRegridder(src, tgt, tgt_location="node")
+
+
 def test_curvilinear_equivalence():
     """
     Test initialisation of :class:`esmf_regrid.schemes.ESMFAreaWeightedRegridder`.