Distance class: remove abc (closes #435)

Fixes undocumented backwards-incompatible change in geopy 2

geopy/distance.py

@@ -115,7 +115,6 @@
 would result in a ``ValueError`` exception.
 
 """
-import abc
 from math import asin, atan2, cos, sin, sqrt
 
 from geographiclib.geodesic import Geodesic
@@ -187,7 +186,7 @@ def _ensure_same_altitude(a, b):
     # it won't give much error.
 
 
-class Distance(abc.ABC):
+class Distance:
 
     def __init__(self, *args, **kwargs):
         kilometers = kwargs.pop('kilometers', 0)
@@ -236,9 +235,8 @@ def __nonzero__(self):
 
     __bool__ = __nonzero__
 
-    @abc.abstractmethod
     def measure(self, a, b):
-        raise NotImplementedError()
+        raise NotImplementedError("Distance is an abstract class")
 
     def __repr__(self):  # pragma: no cover
         return 'Distance(%s)' % self.kilometers

test/test_distance.py

@@ -116,6 +116,11 @@ def test_should_warn_for_mixed_up_lat_lon(self):
                 self.cls((lon, lat), (lon - 10, lat))
             self.assertEqual(1, len(w))
 
+    def test_should_get_consistent_results_for_distance_calculations(self):
+        distance1, distance2 = [self.cls((0, 0), (0, 1))
+                                for _ in range(2)]
+        self.assertEqual(distance1.kilometers, distance2.kilometers)
+
 
 class CommonMathematicalOperatorCases:
 
@@ -164,11 +169,6 @@ def test_should_be_true_in_boolean_context_when_nonzero_length(self):
     def test_should_be_false_in_boolean_context_when_zero_length(self):
         self.assertFalse(self.cls(0))
 
-    def test_should_get_consistent_results_for_distance_calculations(self):
-        distance1, distance2 = [self.cls((0, 0), (0, 1))
-                                for _ in range(2)]
-        self.assertEqual(distance1.kilometers, distance2.kilometers)
-
 
 class CommonConversionCases:
 
@@ -259,13 +259,11 @@ class CommonDistanceCases(CommonDistanceComputationCases,
     pass
 
 
-class TestWhenInstantiatingBaseDistanceClass(unittest.TestCase):
-    def test_should_not_be_able_to_instantiate(self):
-        with self.assertRaises(TypeError):
-            Distance((0, 0), (0, 180))
-
-
-class TestDefaultDistanceClass(unittest.TestCase):
+class TestDefaultDistanceClass(CommonMathematicalOperatorCases,
+                               CommonConversionCases,
+                               CommonComparisonCases,
+                               unittest.TestCase):
+    cls = Distance
 
     def test_default_distance(self):
         self.assertEqual(distance(132).km, 132)