Remove registry args, Add equivalencies

astropy_xarray/conversion.py

@@ -70,7 +70,7 @@ def array_attach_unit(data, unit) -> astropy.units.Quantity:
     return astropy.units.Quantity(data, unit)
 
 
-def array_convert_unit(data, unit) -> astropy.units.Quantity:
+def array_convert_unit(data, unit, equivalencies) -> astropy.units.Quantity:
     """convert the unit of an array
 
     This is roughly the same as ``data.to(unit)``.
@@ -80,8 +80,14 @@ def array_convert_unit(data, unit) -> astropy.units.Quantity:
     data : quantity or array-like
         The data to convert. If it is not a quantity, it is assumed to be
         dimensionless.
-    unit : str or astropy.units.Unit
+    unit : str or astropy.units.UnitBase
         The unit to convert to. If a string ``data`` has to be a quantity.
+    equivalencies : list | None
+        A list of equivalence pairs to try if the units are not
+        directly convertible. See :py:doc:`astropy:units/equivalencies`.
+        This list is in addition to possible global defaults set by,
+        e.g., :py:func:`astropy.units.set_enabled_equivalencies`.
+        Use None to turn off all equivalencies.
 
     Returns
     -------
@@ -95,7 +101,7 @@ def array_convert_unit(data, unit) -> astropy.units.Quantity:
             raise ValueError(f"cannot convert a non-quantity using {unit!r} as unit")
 
         data = (
-            data.to(unit)
+            data.to(unit, equivalencies)
             if isinstance(data, astropy.units.Quantity)
             else astropy.units.Quantity(data, unit)
         )
@@ -239,32 +245,32 @@ def attach_unit_attributes(obj, units, attr="units"):
     return new_obj
 
 
-def convert_units_variable(variable, units):
+def convert_unit_variable(variable, unit, equivalencies):
     if isinstance(variable, IndexVariable):
         if variable.level_names:
             # don't try to convert MultiIndexes
             return variable
 
-        if units is not None:
+        if unit is not None:
             quantity = array_attach_unit(
                 variable.data, variable.attrs.get(unit_attribute_name)
             )
-            converted = array_convert_unit(quantity, units)
+            converted = array_convert_unit(quantity, unit, equivalencies)
             new_obj = variable.copy(data=array_strip_unit(converted))
 
             new_obj.attrs[unit_attribute_name] = array_extract_unit(converted)
         else:
             new_obj = variable
     elif isinstance(variable, Variable):
-        converted = array_convert_unit(variable.data, units)
+        converted = array_convert_unit(variable.data, unit, equivalencies)
         new_obj = variable.copy(data=converted)
     else:
         raise ValueError(f"unknown type: {variable}")
 
     return new_obj
 
 
-def convert_units_index(index, index_vars, units):
+def convert_units_index(index, index_vars, units, equivalencies):
     if not isinstance(index, AstropyIndex):
         raise ValueError("cannot convert non-quantified index")
 
@@ -273,7 +279,7 @@ def convert_units_index(index, index_vars, units):
     for name, var in index_vars.items():
         unit = units.get(name)
         try:
-            converted = convert_units_variable(var, unit)
+            converted = convert_unit_variable(var, unit, equivalencies)
             converted_vars[name] = strip_units_variable(converted)
         except (ValueError, astropy.units.core.UnitConversionError) as e:
             failed[name] = e
@@ -287,7 +293,7 @@ def convert_units_index(index, index_vars, units):
     return AstropyIndex(index=converted_index, units=units)
 
 
-def convert_units_dataset(obj, units):
+def convert_units_dataset(obj, units, equivalencies):
     converted = {}
     failed = {}
     indexed_variables = obj.xindexes.variables
@@ -297,7 +303,7 @@ def convert_units_dataset(obj, units):
 
         unit = units.get(name)
         try:
-            converted[name] = convert_units_variable(var, unit)
+            converted[name] = convert_unit_variable(var, unit, equivalencies)
         except (ValueError, astropy.units.core.UnitConversionError) as e:
             failed[name] = e
 
@@ -308,7 +314,7 @@ def convert_units_dataset(obj, units):
             continue
 
         try:
-            converted_index = convert_units_index(idx, idx_vars, idx_units)
+            converted_index = convert_units_index(idx, idx_vars, idx_units, equivalencies)
             indexes.update({k: converted_index for k in idx_vars})
             index_vars.update(converted_index.create_variables())
         except (ValueError, astropy.units.core.UnitConversionError) as e:
@@ -324,7 +330,7 @@ def convert_units_dataset(obj, units):
     return dataset_from_variables(reordered, obj._coord_names, indexes, obj.attrs)
 
 
-def convert_units(obj, units):
+def convert_units(obj, units, equivalencies):
     if not isinstance(obj, (DataArray, Dataset)):
         raise ValueError(f"cannot convert object: {obj!r}: unknown type")
 
@@ -335,7 +341,7 @@ def convert_units(obj, units):
 
     try:
         new_obj = call_on_dataset(
-            convert_units_dataset, obj, name=temporary_name, units=units
+            convert_units_dataset, obj, name=temporary_name, units=units, equivalencies=equivalencies
         )
     except ValueError as e:
         (failed,) = e.args
@@ -464,27 +470,27 @@ def slice_extract_units(indexer):
         return astropy.units.Quantity(1, units_).si.unit
 
 
-def convert_units_slice(indexer, units):
+def convert_units_slice(indexer, units, equivalencies):
     attrs = {name: getattr(indexer, name) for name in slice_attributes}
     converted = {
-        name: array_convert_unit(value, units) if value is not None else None
+        name: array_convert_unit(value, units, equivalencies) if value is not None else None
         for name, value in attrs.items()
     }
     args = [converted[name] for name in slice_attributes]
 
     return slice(*args)
 
 
-def convert_indexer_units(indexers, units):
+def convert_indexer_units(indexers, units, equivalencies):
     def convert(indexer, units):
         if isinstance(indexer, slice):
-            return convert_units_slice(indexer, units)
+            return convert_units_slice(indexer, units, equivalencies)
         elif isinstance(indexer, DataArray):
-            return convert_units(indexer, {None: units})
+            return convert_units(indexer, {None: units}, equivalencies)
         elif isinstance(indexer, Variable):
-            return convert_units_variable(indexer, units)
+            return convert_unit_variable(indexer, units, equivalencies)
         else:
-            return array_convert_unit(indexer, units)
+            return array_convert_unit(indexer, units, equivalencies)
 
     converted = {}
     invalid = {}

astropy_xarray/index.py

@@ -67,8 +67,8 @@ def stack(cls, variables, dim):
     def unstack(self):
         raise NotImplementedError()
 
-    def sel(self, labels, **options):
-        converted_labels = conversion.convert_indexer_units(labels, self.units)
+    def sel(self, labels, equivalencies=None, **options):
+        converted_labels = conversion.convert_indexer_units(labels, self.units, equivalencies)
         stripped_labels = conversion.strip_indexer_units(converted_labels)
 
         return self.index.sel(stripped_labels, **options)