fix dimensionality comparison bug #386208 caused by hash(-1)==hash(-2)

ddale · ddale · commit 522c06ac16d1 · 2009-06-18T17:17:32.000-04:00
Thanks Tony Yu for the bug report and suggested fix
diff --git a/quantities/dimensionality.py b/quantities/dimensionality.py
@@ -53,6 +53,9 @@ def __hash__(self):
         res = hash(unit_registry['dimensionless'])
         for key in sorted(self.keys(), key=operator.attrgetter('format_order')):
             val = self[key]
+            if val < 0:
+                # can you believe that hash(-1)==hash(-2)?
+                val -= 1
             res ^= hash((key, val))
         return res
 
diff --git a/quantities/tests/test_01_dimensionality.py b/quantities/tests/test_01_dimensionality.py
@@ -141,6 +141,7 @@ def test_power():
     assert_equal(joule**2, Dimensionality({pq.kg: 2, pq.m: 4, pq.s: -4}))
     assert_raises(TypeError, operator.__pow__, Joule, joule)
     assert_raises(TypeError, operator.__pow__, joule, Joule)
+    assert_equal(meter**-1 == meter**-2, False)
     test_dimensionality_repr()
 
 def test_inplace_power():
