Issue #13121: Support in-place math operators for collections.Counter().
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index 04c4d97..ec20938 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -932,6 +932,27 @@
set_result = setop(set(p.elements()), set(q.elements()))
self.assertEqual(counter_result, dict.fromkeys(set_result, 1))
+ def test_inplace_operations(self):
+ elements = 'abcd'
+ for i in range(1000):
+ # test random pairs of multisets
+ p = Counter(dict((elem, randrange(-2,4)) for elem in elements))
+ p.update(e=1, f=-1, g=0)
+ q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
+ q.update(h=1, i=-1, j=0)
+ for inplace_op, regular_op in [
+ (Counter.__iadd__, Counter.__add__),
+ (Counter.__isub__, Counter.__sub__),
+ (Counter.__ior__, Counter.__or__),
+ (Counter.__iand__, Counter.__and__),
+ ]:
+ c = p.copy()
+ c_id = id(c)
+ regular_result = regular_op(c, q)
+ inplace_result = inplace_op(c, q)
+ self.assertEqual(inplace_result, regular_result)
+ self.assertEqual(id(inplace_result), c_id)
+
def test_subtract(self):
c = Counter(a=-5, b=0, c=5, d=10, e=15,g=40)
c.subtract(a=1, b=2, c=-3, d=10, e=20, f=30, h=-50)