bpo-40755: Add rich comparisons to Counter (GH-20548)
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index ea2b420..f538da5 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -290,47 +290,6 @@
>>> sorted(c.elements())
['a', 'a', 'a', 'a', 'b', 'b']
- .. method:: isdisjoint(other)
-
- True if none of the elements in *self* overlap with those in *other*.
- Negative or missing counts are ignored.
- Logically equivalent to: ``not (+self) & (+other)``
-
- .. versionadded:: 3.10
-
- .. method:: isequal(other)
-
- Test whether counts agree exactly.
- Negative or missing counts are treated as zero.
-
- This method works differently than the inherited :meth:`__eq__` method
- which treats negative or missing counts as distinct from zero::
-
- >>> Counter(a=1, b=0).isequal(Counter(a=1))
- True
- >>> Counter(a=1, b=0) == Counter(a=1)
- False
-
- Logically equivalent to: ``+self == +other``
-
- .. versionadded:: 3.10
-
- .. method:: issubset(other)
-
- True if the counts in *self* are less than or equal to those in *other*.
- Negative or missing counts are treated as zero.
- Logically equivalent to: ``not self - (+other)``
-
- .. versionadded:: 3.10
-
- .. method:: issuperset(other)
-
- True if the counts in *self* are greater than or equal to those in *other*.
- Negative or missing counts are treated as zero.
- Logically equivalent to: ``not other - (+self)``
-
- .. versionadded:: 3.10
-
.. method:: most_common([n])
Return a list of the *n* most common elements and their counts from the
@@ -369,6 +328,19 @@
instead of replacing them. Also, the *iterable* is expected to be a
sequence of elements, not a sequence of ``(key, value)`` pairs.
+Counters support rich comparison operators for equality, subset, and
+superset relationships: ``==``, ``!=``, ``<``, ``<=``, ``>``, ``>=``.
+All of those tests treat missing elements as having zero counts so that
+``Counter(a=1) == Counter(a=1, b=0)`` returns true.
+
+.. versionadded:: 3.10
+ Rich comparison operations we were added
+
+.. versionchanged:: 3.10
+ In equality tests, missing elements are treated as having zero counts.
+ Formerly, ``Counter(a=3)`` and ``Counter(a=3, b=0)`` were considered
+ distinct.
+
Common patterns for working with :class:`Counter` objects::
sum(c.values()) # total of all counts
diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index 55fb46c..2acf672 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -691,6 +691,42 @@
if elem in self:
super().__delitem__(elem)
+ def __eq__(self, other):
+ 'True if all counts agree. Missing counts are treated as zero.'
+ if not isinstance(other, Counter):
+ return NotImplemented
+ return all(self[e] == other[e] for c in (self, other) for e in c)
+
+ def __ne__(self, other):
+ 'True if any counts disagree. Missing counts are treated as zero.'
+ if not isinstance(other, Counter):
+ return NotImplemented
+ return not self == other
+
+ def __le__(self, other):
+ 'True if all counts in self are a subset of those in other.'
+ if not isinstance(other, Counter):
+ return NotImplemented
+ return all(self[e] <= other[e] for c in (self, other) for e in c)
+
+ def __lt__(self, other):
+ 'True if all counts in self are a proper subset of those in other.'
+ if not isinstance(other, Counter):
+ return NotImplemented
+ return self <= other and self != other
+
+ def __ge__(self, other):
+ 'True if all counts in self are a superset of those in other.'
+ if not isinstance(other, Counter):
+ return NotImplemented
+ return all(self[e] >= other[e] for c in (self, other) for e in c)
+
+ def __gt__(self, other):
+ 'True if all counts in self are a proper superset of those in other.'
+ if not isinstance(other, Counter):
+ return NotImplemented
+ return self >= other and self != other
+
def __repr__(self):
if not self:
return '%s()' % self.__class__.__name__
@@ -886,92 +922,6 @@
self[elem] = other_count
return self._keep_positive()
- def isequal(self, other):
- ''' Test whether counts agree exactly.
-
- Negative or missing counts are treated as zero.
-
- This is different than the inherited __eq__() method which
- treats negative or missing counts as distinct from zero:
-
- >>> Counter(a=1, b=0).isequal(Counter(a=1))
- True
- >>> Counter(a=1, b=0) == Counter(a=1)
- False
-
- Logically equivalent to: +self == +other
- '''
- if not isinstance(other, Counter):
- other = Counter(other)
- for elem in set(self) | set(other):
- left = self[elem]
- right = other[elem]
- if left == right:
- continue
- if left < 0:
- left = 0
- if right < 0:
- right = 0
- if left != right:
- return False
- return True
-
- def issubset(self, other):
- '''True if the counts in self are less than or equal to those in other.
-
- Negative or missing counts are treated as zero.
-
- Logically equivalent to: not self - (+other)
- '''
- if not isinstance(other, Counter):
- other = Counter(other)
- for elem, count in self.items():
- other_count = other[elem]
- if other_count < 0:
- other_count = 0
- if count > other_count:
- return False
- return True
-
- def issuperset(self, other):
- '''True if the counts in self are greater than or equal to those in other.
-
- Negative or missing counts are treated as zero.
-
- Logically equivalent to: not other - (+self)
- '''
- if not isinstance(other, Counter):
- other = Counter(other)
- return other.issubset(self)
-
- def isdisjoint(self, other):
- '''True if none of the elements in self overlap with those in other.
-
- Negative or missing counts are ignored.
-
- Logically equivalent to: not (+self) & (+other)
- '''
- if not isinstance(other, Counter):
- other = Counter(other)
- for elem, count in self.items():
- if count > 0 and other[elem] > 0:
- return False
- return True
-
- # Rich comparison operators for multiset subset and superset tests
- # have been deliberately omitted due to semantic conflicts with the
- # existing inherited dict equality method. Subset and superset
- # semantics ignore zero counts and require that p⊆q ∧ p⊇q ⇔ p=q;
- # however, that would not be the case for p=Counter(a=1, b=0)
- # and q=Counter(a=1) where the dictionaries are not equal.
-
- def _omitted(self, other):
- raise TypeError(
- 'Rich comparison operators have been deliberately omitted. '
- 'Use the isequal(), issubset(), and issuperset() methods instead.')
-
- __lt__ = __le__ = __gt__ = __ge__ = __lt__ = _omitted
-
########################################################################
### ChainMap
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index 8d80e88..7c7f865 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -2123,29 +2123,6 @@
set_result = setop(set(p.elements()), set(q.elements()))
self.assertEqual(counter_result, dict.fromkeys(set_result, 1))
- def test_subset_superset_not_implemented(self):
- # Verify that multiset comparison operations are not implemented.
-
- # These operations were intentionally omitted because multiset
- # comparison semantics conflict with existing dict equality semantics.
-
- # For multisets, we would expect that if p<=q and p>=q are both true,
- # then p==q. However, dict equality semantics require that p!=q when
- # one of sets contains an element with a zero count and the other
- # doesn't.
-
- p = Counter(a=1, b=0)
- q = Counter(a=1, c=0)
- self.assertNotEqual(p, q)
- with self.assertRaises(TypeError):
- p < q
- with self.assertRaises(TypeError):
- p <= q
- with self.assertRaises(TypeError):
- p > q
- with self.assertRaises(TypeError):
- p >= q
-
def test_inplace_operations(self):
elements = 'abcd'
for i in range(1000):
@@ -2234,49 +2211,32 @@
self.assertEqual(set(cp - cq), sp - sq)
self.assertEqual(set(cp | cq), sp | sq)
self.assertEqual(set(cp & cq), sp & sq)
- self.assertEqual(cp.isequal(cq), sp == sq)
- self.assertEqual(cp.issubset(cq), sp.issubset(sq))
- self.assertEqual(cp.issuperset(cq), sp.issuperset(sq))
- self.assertEqual(cp.isdisjoint(cq), sp.isdisjoint(sq))
+ self.assertEqual(cp == cq, sp == sq)
+ self.assertEqual(cp != cq, sp != sq)
+ self.assertEqual(cp <= cq, sp <= sq)
+ self.assertEqual(cp >= cq, sp >= sq)
+ self.assertEqual(cp < cq, sp < sq)
+ self.assertEqual(cp > cq, sp > sq)
- def test_multiset_equal(self):
- self.assertTrue(Counter(a=3, b=2, c=0).isequal('ababa'))
- self.assertFalse(Counter(a=3, b=2).isequal('babab'))
+ def test_eq(self):
+ self.assertEqual(Counter(a=3, b=2, c=0), Counter('ababa'))
+ self.assertNotEqual(Counter(a=3, b=2), Counter('babab'))
- def test_multiset_subset(self):
- self.assertTrue(Counter(a=3, b=2, c=0).issubset('ababa'))
- self.assertFalse(Counter(a=3, b=2).issubset('babab'))
+ def test_le(self):
+ self.assertTrue(Counter(a=3, b=2, c=0) <= Counter('ababa'))
+ self.assertFalse(Counter(a=3, b=2) <= Counter('babab'))
- def test_multiset_superset(self):
- self.assertTrue(Counter(a=3, b=2, c=0).issuperset('aab'))
- self.assertFalse(Counter(a=3, b=2, c=0).issuperset('aabd'))
+ def test_lt(self):
+ self.assertTrue(Counter(a=3, b=1, c=0) < Counter('ababa'))
+ self.assertFalse(Counter(a=3, b=2, c=0) < Counter('ababa'))
- def test_multiset_disjoint(self):
- self.assertTrue(Counter(a=3, b=2, c=0).isdisjoint('cde'))
- self.assertFalse(Counter(a=3, b=2, c=0).isdisjoint('bcd'))
+ def test_ge(self):
+ self.assertTrue(Counter(a=2, b=1, c=0) >= Counter('aab'))
+ self.assertFalse(Counter(a=3, b=2, c=0) >= Counter('aabd'))
- def test_multiset_predicates_with_negative_counts(self):
- # Multiset predicates run on the output of the elements() method,
- # meaning that zero counts and negative counts are ignored.
- # The tests below confirm that we get that same results as the
- # tests above, even after a negative count has been included
- # in either *self* or *other*.
- self.assertTrue(Counter(a=3, b=2, c=0, d=-1).isequal('ababa'))
- self.assertFalse(Counter(a=3, b=2, d=-1).isequal('babab'))
- self.assertTrue(Counter(a=3, b=2, c=0, d=-1).issubset('ababa'))
- self.assertFalse(Counter(a=3, b=2, d=-1).issubset('babab'))
- self.assertTrue(Counter(a=3, b=2, c=0, d=-1).issuperset('aab'))
- self.assertFalse(Counter(a=3, b=2, c=0, d=-1).issuperset('aabd'))
- self.assertTrue(Counter(a=3, b=2, c=0, d=-1).isdisjoint('cde'))
- self.assertFalse(Counter(a=3, b=2, c=0, d=-1).isdisjoint('bcd'))
- self.assertTrue(Counter(a=3, b=2, c=0, d=-1).isequal(Counter(a=3, b=2, c=-1)))
- self.assertFalse(Counter(a=3, b=2, d=-1).isequal(Counter(a=2, b=3, c=-1)))
- self.assertTrue(Counter(a=3, b=2, c=0, d=-1).issubset(Counter(a=3, b=2, c=-1)))
- self.assertFalse(Counter(a=3, b=2, d=-1).issubset(Counter(a=2, b=3, c=-1)))
- self.assertTrue(Counter(a=3, b=2, c=0, d=-1).issuperset(Counter(a=2, b=1, c=-1)))
- self.assertFalse(Counter(a=3, b=2, c=0, d=-1).issuperset(Counter(a=2, b=1, c=-1, d=1)))
- self.assertTrue(Counter(a=3, b=2, c=0, d=-1).isdisjoint(Counter(c=1, d=2, e=3, f=-1)))
- self.assertFalse(Counter(a=3, b=2, c=0, d=-1).isdisjoint(Counter(b=1, c=1, d=1, e=-1)))
+ def test_gt(self):
+ self.assertTrue(Counter(a=3, b=2, c=0) > Counter('aab'))
+ self.assertFalse(Counter(a=2, b=1, c=0) > Counter('aab'))
################################################################################
diff --git a/Misc/NEWS.d/next/Library/2020-05-23-18-24-13.bpo-22533.k64XGo.rst b/Misc/NEWS.d/next/Library/2020-05-23-18-24-13.bpo-22533.k64XGo.rst
deleted file mode 100644
index 737162f..0000000
--- a/Misc/NEWS.d/next/Library/2020-05-23-18-24-13.bpo-22533.k64XGo.rst
+++ /dev/null
@@ -1,2 +0,0 @@
-Add multiset comparison methods to collections.Counter(): isequal(),
-issubset(), issuperset(), and isdisjoint().
diff --git a/Misc/NEWS.d/next/Library/2020-05-30-18-48-58.bpo-40755.IyOe2J.rst b/Misc/NEWS.d/next/Library/2020-05-30-18-48-58.bpo-40755.IyOe2J.rst
new file mode 100644
index 0000000..be5653e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-05-30-18-48-58.bpo-40755.IyOe2J.rst
@@ -0,0 +1 @@
+Add rich comparisons to collections.Counter().