Fix #1189

Make is_compatible_with function with dimensionless types & string parsing errors.
is_compatible_with was not consistent with dimensionless types when switching arguments.
String processing was not allowing strings with any magnitude.

- Updated registry.py managing dimensionless types & discarding types not managed by pint.
- Updated unit.py using parse_expression instead of parse_units.

CHANGES

@@ -4,7 +4,7 @@ Pint Changelog
 0.17 (unreleased)
 -----------------
 
-- Nothing changed yet.
+- Fix bugs on `is_compatible_with` with dimensionless types & string parsing errors. (Issue #1189)
 
 
 0.16.1 (2020-09-22)

pint/quantity.py

@@ -597,7 +597,8 @@ def is_compatible_with(self, other, *contexts, **ctx_kwargs):
 
         if isinstance(other, str):
             return (
-                self.dimensionality == self._REGISTRY.parse_units(other).dimensionality
+                self.dimensionality
+                == self._REGISTRY.parse_expression(other).dimensionality
             )
 
         return self.dimensionless

pint/registry.py

@@ -914,6 +914,11 @@ def is_compatible_with(self, obj1, obj2, *contexts, **ctx_kwargs):
         -------
         bool
         """
+        if isinstance(obj1, (dict, bool, type(None))) or isinstance(
+            obj2, (dict, bool, type(None))
+        ):
+            raise TypeError("Type can't be casted to Quantity")
+
         if isinstance(obj1, (self.Quantity, self.Unit)):
             return obj1.is_compatible_with(obj2, *contexts, **ctx_kwargs)
 
@@ -922,7 +927,10 @@ def is_compatible_with(self, obj1, obj2, *contexts, **ctx_kwargs):
                 obj2, *contexts, **ctx_kwargs
             )
 
-        return not isinstance(obj2, (self.Quantity, self.Unit))
+        if isinstance(obj2, (self.Quantity, self.Unit, str)):
+            return self.is_compatible_with(obj2, obj1, *contexts, **ctx_kwargs)
+        else:
+            return self.Quantity(obj1).is_compatible_with(obj2, *contexts, **ctx_kwargs)
 
     def convert(self, value, src, dst, inplace=False):
         """Convert value from some source to destination units.

pint/testsuite/test_unit.py

@@ -3,6 +3,8 @@
 import math
 import re
 
+import pytest
+
 from pint import (
     DefinitionSyntaxError,
     DimensionalityError,
@@ -12,6 +14,7 @@
 from pint.compat import np
 from pint.registry import LazyRegistry, UnitRegistry
 from pint.testsuite import CaseInsensitveQuantityTestCase, QuantityTestCase, helpers
+from pint.testsuite.helpers import requires_numpy
 from pint.testsuite.parameterized import ParameterizedTestCase
 from pint.util import ParserHelper, UnitsContainer
 
@@ -724,6 +727,34 @@ def test_case_sensitivity(self):
             ureg.parse_units("j", case_sensitive=False), UnitsContainer(joule=1)
         )
 
+    @requires_numpy()
+    def test_is_compatible_with(self):
+        ureg = self.ureg
+
+        assert ureg.is_compatible_with(ureg.deg, 10.0)
+        assert ureg.is_compatible_with(10.0, ureg.deg)
+        assert ureg.is_compatible_with(ureg.km, ureg.m)
+        assert ureg.is_compatible_with([1, 2, 3, 4], 10.0)
+        assert ureg.is_compatible_with(np.array([1, 2, 3, 4]), ureg.deg)
+        assert ureg.is_compatible_with(10.0, np.array([1, 2, 3, 4]))
+        assert ureg.is_compatible_with(999.0, 10.0)
+        assert ureg.is_compatible_with("80 in", "35000 ft")
+        assert ureg.is_compatible_with("in", "35000 ft")
+        assert ureg.is_compatible_with("in", "ft")
+        assert ureg.is_compatible_with("3500 in", "ft")
+        assert ureg.is_compatible_with(ureg.m, "35000 ft")
+
+        assert not ureg.is_compatible_with(10.0, ureg.m)
+        assert not ureg.is_compatible_with(ureg.m, 10.0)
+        assert not ureg.is_compatible_with(ureg.m, "1 N")
+        assert not ureg.is_compatible_with("1 N", ureg.m)
+
+        assert ureg.is_compatible_with(ureg.hertz, ureg.nm, "spectroscopy")
+        with pytest.raises(TypeError):
+            ureg.is_compatible_with({}, {})
+            ureg.is_compatible_with(None, ureg.deg)
+            ureg.is_compatible_with(True, ureg.deg)
+
 
 class TestCaseInsensitiveRegistry(CaseInsensitveQuantityTestCase):
     def test_case_sensitivity(self):

pint/unit.py

@@ -169,7 +169,8 @@ def is_compatible_with(self, other, *contexts, **ctx_kwargs):
 
         if isinstance(other, str):
             return (
-                self.dimensionality == self._REGISTRY.parse_units(other).dimensionality
+                self.dimensionality
+                == self._REGISTRY.parse_expression(other).dimensionality
             )
 
         return self.dimensionless