Add parse_units_as_container to homogeneize input/ouput in registry f…

…unctions public and private functions

pint/facets/nonmultiplicative/registry.py

@@ -57,7 +57,7 @@ def __init__(
         # plain units on multiplication and division.
         self.autoconvert_offset_to_baseunit = autoconvert_offset_to_baseunit
 
-    def _parse_units(
+    def parse_units_as_container(
         self,
         input_string: str,
         as_delta: Optional[bool] = None,
@@ -67,7 +67,7 @@ def _parse_units(
         if as_delta is None:
             as_delta = self.default_as_delta
 
-        return super()._parse_units(input_string, as_delta, case_sensitive)
+        return super().parse_units_as_container(input_string, as_delta, case_sensitive)
 
     def _add_unit(self, definition: UnitDefinition) -> None:
         super()._add_unit(definition)

pint/facets/plain/registry.py

@@ -1185,14 +1185,29 @@ def parse_units(
 
         """
 
-        units = self._parse_units(input_string, as_delta, case_sensitive)
-        return self.Unit(units)
+        return self.Unit(
+            self.parse_units_as_container(input_string, as_delta, case_sensitive)
+        )
 
-    def _parse_units(
+    def parse_units_as_container(
         self,
         input_string: str,
-        as_delta: bool = True,
+        as_delta: Optional[bool] = None,
         case_sensitive: Optional[bool] = None,
+    ) -> UnitsContainer:
+        as_delta = (
+            as_delta if as_delta is not None else True
+        )  # TODO This only exists in nonmultiplicative
+        case_sensitive = (
+            case_sensitive if case_sensitive is not None else self.case_sensitive
+        )
+        return self._parse_units_as_container(input_string, as_delta, case_sensitive)
+
+    def _parse_units_as_container(
+        self,
+        input_string: str,
+        as_delta: bool = True,
+        case_sensitive: bool = True,
     ) -> UnitsContainer:
         """Parse a units expression and returns a UnitContainer with
         the canonical names.

pint/util.py

@@ -1043,8 +1043,7 @@ def to_units_container(
             # TODO: document how to whether to lift preprocessing loop out to caller
             for p in registry.preprocessors:
                 unit_like = p(unit_like)
-            # TODO: Why not parse.units here?
-            return registry._parse_units(unit_like)
+            return registry.parse_units_as_container(unit_like)
         else:
             return ParserHelper.from_string(unit_like)
     elif dict in mro: