Fix unnecessary sorting and copying in __hash__ (#52)

* Fix unnecessary sorting and copying in __hash__ #51 * Use frozenset hash instead of summing per feedback on #52 (review) Co-authored-by: MikeFHay <>
wheerd · Dec 6, 2021 · 16c8717 · 16c8717
1 parent 0dba7f9
commit 16c8717
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Showing 2 changed files with 3 additions and 5 deletions.
diff --git a/multiset.py b/multiset.py
@@ -1078,8 +1078,7 @@ class FrozenMultiset(BaseMultiset):
     __slots__ = ()
 
     def __hash__(self):
-        return hash(tuple(sorted(self._elements.items())))
-
+        return hash(frozenset(self._elements.items()))
 
 Mapping.register(BaseMultiset)  # type: ignore
 MutableMapping.register(Multiset)  # type: ignore

diff --git a/tests/test_multiset.py b/tests/test_multiset.py
@@ -968,11 +968,10 @@ def test_base_error():
 
 def test_frozen_hash_equal():
     ms1 = FrozenMultiset('ab')
-    ms2 = FrozenMultiset('ab')
+    ms2 = FrozenMultiset('ba')
 
     assert hash(ms1) == hash(ms2)
 
-
 def test_can_be_pickled():
     fms = FrozenMultiset('aabcd')
 
@@ -1001,4 +1000,4 @@ def test_multiplicities(MultisetCls):
 
 def test_distinct_elements(MultisetCls):
     ms = MultisetCls('aaabbc')
-    assert sorted(ms.distinct_elements()) == list('abc')
+    assert sorted(ms.distinct_elements()) == list('abc')