Detailed Error Message for get_dimensionality() (#1874)

CHANGES

@@ -49,6 +49,8 @@ Pint Changelog
  (PR #1819)
 - Add numpy.linalg.norm implementation.
  (PR #1251)
+- Improved error message in `get_dimensionality()` when non existent units are passed.
+ (PR #1874, Issue #1716)
 
 0.22 (2023-05-25)
 -----------------

pint/facets/plain/registry.py

@@ -736,7 +736,12 @@ def _get_dimensionality_recurse(
  for key in ref:
  exp2 = exp * ref[key]
  if _is_dim(key):
- reg = self._dimensions[key]
+ try:
+ reg = self._dimensions[key]
+ except KeyError:
+ raise ValueError(
+ f"{key} is not defined as dimension in the pint UnitRegistry"
+ )
  if isinstance(reg, DerivedDimensionDefinition):
  self._get_dimensionality_recurse(reg.reference, exp2, accumulator)
  else:

pint/testsuite/test_errors.py

@@ -144,3 +144,13 @@ def test_pickle_definition_syntax_error(self, subtests):
 
  with pytest.raises(PintError):
  raise ex
+
+ def test_dimensionality_error_message(self):
+ ureg = UnitRegistry(system="SI")
+ with pytest.raises(ValueError) as error:
+ ureg.get_dimensionality("[bilbo]")
+
+ assert (
+ str(error.value)
+ == "[bilbo] is not defined as dimension in the pint UnitRegistry"
+ )