Adding a new UnitConverter Unity()

Following the discussion in #2410

Author: erikvansebille

src/parcels/__init__.py

@@ -14,7 +14,7 @@
     GeographicPolar,
     GeographicPolarSquare,
     GeographicSquare,
-    UnitConverter,
+    Unity,
 )
 from parcels._core.field import Field, VectorField
 from parcels._core.fieldset import FieldSet
@@ -66,7 +66,7 @@
     "GeographicPolar",
     "GeographicPolarSquare",
     "GeographicSquare",
-    "UnitConverter",
+    "Unity",
     # Status codes and errors
     "AllParcelsErrorCodes",
     "FieldInterpolationError",

src/parcels/_core/converters.py

@@ -11,6 +11,7 @@
     "GeographicPolarSquare",
     "GeographicSquare",
     "UnitConverter",
+    "Unity",
     "_convert_to_flat_array",
     "_unitconverters_map",
 ]
@@ -28,11 +29,16 @@ def _convert_to_flat_array(var: npt.ArrayLike) -> npt.NDArray:
 
 
 class UnitConverter:
-    """Interface class for spatial unit conversion during field sampling that performs no conversion."""
-
     source_unit: str | None = None
     target_unit: str | None = None
 
+
+class Unity(UnitConverter):
+    """Interface class for spatial unit conversion during field sampling that performs no conversion."""
+
+    source_unit: None
+    target_unit: None
+
     def to_target(self, value, z, y, x):
         return value
 

src/parcels/_core/field.py

@@ -10,6 +10,7 @@
 
 from parcels._core.converters import (
     UnitConverter,
+    Unity,
     _unitconverters_map,
 )
 from parcels._core.index_search import GRID_SEARCH_ERROR, LEFT_OUT_OF_BOUNDS, RIGHT_OUT_OF_BOUNDS, _search_time_index
@@ -135,7 +136,7 @@ def __init__(
         self.igrid = -1  # Default the grid index to -1
 
         if self.grid._mesh == "flat" or (self.name not in _unitconverters_map.keys()):
-            self.units = UnitConverter()
+            self.units = Unity()
         elif self.grid._mesh == "spherical":
             self.units = _unitconverters_map[self.name]
 

tests-v3/test_fieldset.py

@@ -13,7 +13,7 @@
     Variable,
 )
 from parcels.field import VectorField
-from parcels.tools.converters import GeographicPolar, UnitConverter
+from parcels.tools.converters import GeographicPolar, Unity
 from tests.utils import TEST_DATA
 
 
@@ -119,7 +119,7 @@ def test_field_from_netcdf_fieldtypes():
 
     # first try without setting fieldtype
     fset = FieldSet.from_nemo(filenames, variables, dimensions)
-    assert isinstance(fset.varU.units, UnitConverter)
+    assert isinstance(fset.varU.units, Unity)
 
     # now try with setting fieldtype
     fset = FieldSet.from_nemo(filenames, variables, dimensions, fieldtype={"varU": "U", "varV": "V"})