Merge #524

524: Fix for Issue #523 r=hgrecco
Conversion to/from offset units was not checking for compatibility of dimensions.
A test for the issue was added.

pint/registry.py

@@ -935,6 +935,11 @@ class NonMultiplicativeRegistry(BaseRegistry):
         src_dim = self._get_dimensionality(src)
         dst_dim = self._get_dimensionality(dst)
 
+        # If the source and destination dimensionality are different,
+        # then the conversion cannot be performed.
+        if src_dim != dst_dim:
+            raise DimensionalityError(src, dst, src_dim, dst_dim)
+
         # For offset units we need to check if the conversion is allowed.
         if src_offset_units or dst_offset_units:
 

pint/testsuite/test_issues.py

@@ -10,7 +10,7 @@ from pint.unit import UnitsContainer
 from pint.util import ParserHelper
 
 from pint.compat import np, long_type
-from pint.errors import UndefinedUnitError
+from pint.errors import UndefinedUnitError, DimensionalityError
 from pint.testsuite import QuantityTestCase, helpers
 from pint.testsuite.compat import unittest
 
@@ -205,6 +205,14 @@ class TestIssues(QuantityTestCase):
         self.assertQuantityAlmostEqual(x + y, 5.1 * ureg.meter)
         self.assertQuantityAlmostEqual(z, 5.1 * ureg.meter)
 
+    def test_issue523(self):
+        ureg = UnitRegistry()
+        src, dst = UnitsContainer({'meter': 1}), UnitsContainer({'degF': 1})
+        value = 10.
+        convert = self.ureg.convert
+        self.assertRaises(DimensionalityError, convert, value, src, dst)
+        self.assertRaises(DimensionalityError, convert, value, dst, src)
+
     def _test_issueXX(self):
         ureg = UnitRegistry()
         try: