bpo-40755: Add rich comparisons to Counter (GH-20548)
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Raymond Hettinger
GitHub
parent
2b201369b4
commit
b7d79b4f36
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@ -290,47 +290,6 @@ For example::
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>>> sorted(c.elements())
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['a', 'a', 'a', 'a', 'b', 'b']
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.. method:: isdisjoint(other)
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True if none of the elements in *self* overlap with those in *other*.
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Negative or missing counts are ignored.
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Logically equivalent to: ``not (+self) & (+other)``
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.. versionadded:: 3.10
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.. method:: isequal(other)
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Test whether counts agree exactly.
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Negative or missing counts are treated as zero.
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This method works differently than the inherited :meth:`__eq__` method
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which treats negative or missing counts as distinct from zero::
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>>> Counter(a=1, b=0).isequal(Counter(a=1))
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True
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>>> Counter(a=1, b=0) == Counter(a=1)
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False
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Logically equivalent to: ``+self == +other``
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.. versionadded:: 3.10
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.. method:: issubset(other)
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True if the counts in *self* are less than or equal to those in *other*.
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Negative or missing counts are treated as zero.
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Logically equivalent to: ``not self - (+other)``
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.. versionadded:: 3.10
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.. method:: issuperset(other)
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True if the counts in *self* are greater than or equal to those in *other*.
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Negative or missing counts are treated as zero.
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Logically equivalent to: ``not other - (+self)``
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.. versionadded:: 3.10
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.. method:: most_common([n])
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Return a list of the *n* most common elements and their counts from the
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@ -369,6 +328,19 @@ For example::
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instead of replacing them. Also, the *iterable* is expected to be a
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sequence of elements, not a sequence of ``(key, value)`` pairs.
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Counters support rich comparison operators for equality, subset, and
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superset relationships: ``==``, ``!=``, ``<``, ``<=``, ``>``, ``>=``.
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All of those tests treat missing elements as having zero counts so that
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``Counter(a=1) == Counter(a=1, b=0)`` returns true.
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.. versionadded:: 3.10
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Rich comparison operations we were added
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.. versionchanged:: 3.10
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In equality tests, missing elements are treated as having zero counts.
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Formerly, ``Counter(a=3)`` and ``Counter(a=3, b=0)`` were considered
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distinct.
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Common patterns for working with :class:`Counter` objects::
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sum(c.values()) # total of all counts
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@ -691,6 +691,42 @@ class Counter(dict):
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if elem in self:
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super().__delitem__(elem)
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def __eq__(self, other):
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'True if all counts agree. Missing counts are treated as zero.'
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if not isinstance(other, Counter):
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return NotImplemented
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return all(self[e] == other[e] for c in (self, other) for e in c)
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def __ne__(self, other):
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'True if any counts disagree. Missing counts are treated as zero.'
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if not isinstance(other, Counter):
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return NotImplemented
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return not self == other
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def __le__(self, other):
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'True if all counts in self are a subset of those in other.'
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if not isinstance(other, Counter):
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return NotImplemented
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return all(self[e] <= other[e] for c in (self, other) for e in c)
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def __lt__(self, other):
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'True if all counts in self are a proper subset of those in other.'
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if not isinstance(other, Counter):
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return NotImplemented
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return self <= other and self != other
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def __ge__(self, other):
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'True if all counts in self are a superset of those in other.'
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if not isinstance(other, Counter):
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return NotImplemented
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return all(self[e] >= other[e] for c in (self, other) for e in c)
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def __gt__(self, other):
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'True if all counts in self are a proper superset of those in other.'
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if not isinstance(other, Counter):
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return NotImplemented
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return self >= other and self != other
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def __repr__(self):
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if not self:
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return '%s()' % self.__class__.__name__
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@ -886,92 +922,6 @@ class Counter(dict):
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self[elem] = other_count
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return self._keep_positive()
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def isequal(self, other):
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''' Test whether counts agree exactly.
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Negative or missing counts are treated as zero.
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This is different than the inherited __eq__() method which
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treats negative or missing counts as distinct from zero:
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>>> Counter(a=1, b=0).isequal(Counter(a=1))
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True
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>>> Counter(a=1, b=0) == Counter(a=1)
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False
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Logically equivalent to: +self == +other
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'''
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if not isinstance(other, Counter):
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other = Counter(other)
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for elem in set(self) | set(other):
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left = self[elem]
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right = other[elem]
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if left == right:
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continue
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if left < 0:
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left = 0
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if right < 0:
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right = 0
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if left != right:
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return False
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return True
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def issubset(self, other):
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'''True if the counts in self are less than or equal to those in other.
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Negative or missing counts are treated as zero.
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Logically equivalent to: not self - (+other)
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'''
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if not isinstance(other, Counter):
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other = Counter(other)
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for elem, count in self.items():
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other_count = other[elem]
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if other_count < 0:
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other_count = 0
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if count > other_count:
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return False
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return True
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def issuperset(self, other):
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'''True if the counts in self are greater than or equal to those in other.
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Negative or missing counts are treated as zero.
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Logically equivalent to: not other - (+self)
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'''
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if not isinstance(other, Counter):
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other = Counter(other)
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return other.issubset(self)
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def isdisjoint(self, other):
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'''True if none of the elements in self overlap with those in other.
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Negative or missing counts are ignored.
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Logically equivalent to: not (+self) & (+other)
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'''
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if not isinstance(other, Counter):
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other = Counter(other)
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for elem, count in self.items():
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if count > 0 and other[elem] > 0:
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return False
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return True
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# Rich comparison operators for multiset subset and superset tests
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# have been deliberately omitted due to semantic conflicts with the
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# existing inherited dict equality method. Subset and superset
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# semantics ignore zero counts and require that p⊆q ∧ p⊇q ⇔ p=q;
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# however, that would not be the case for p=Counter(a=1, b=0)
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# and q=Counter(a=1) where the dictionaries are not equal.
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def _omitted(self, other):
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raise TypeError(
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'Rich comparison operators have been deliberately omitted. '
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'Use the isequal(), issubset(), and issuperset() methods instead.')
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__lt__ = __le__ = __gt__ = __ge__ = __lt__ = _omitted
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########################################################################
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### ChainMap
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@ -2123,29 +2123,6 @@ class TestCounter(unittest.TestCase):
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set_result = setop(set(p.elements()), set(q.elements()))
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self.assertEqual(counter_result, dict.fromkeys(set_result, 1))
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def test_subset_superset_not_implemented(self):
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# Verify that multiset comparison operations are not implemented.
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# These operations were intentionally omitted because multiset
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# comparison semantics conflict with existing dict equality semantics.
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# For multisets, we would expect that if p<=q and p>=q are both true,
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# then p==q. However, dict equality semantics require that p!=q when
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# one of sets contains an element with a zero count and the other
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# doesn't.
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p = Counter(a=1, b=0)
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q = Counter(a=1, c=0)
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self.assertNotEqual(p, q)
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with self.assertRaises(TypeError):
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p < q
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with self.assertRaises(TypeError):
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p <= q
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with self.assertRaises(TypeError):
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p > q
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with self.assertRaises(TypeError):
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p >= q
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def test_inplace_operations(self):
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elements = 'abcd'
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for i in range(1000):
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@ -2234,49 +2211,32 @@ class TestCounter(unittest.TestCase):
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self.assertEqual(set(cp - cq), sp - sq)
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self.assertEqual(set(cp | cq), sp | sq)
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self.assertEqual(set(cp & cq), sp & sq)
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self.assertEqual(cp.isequal(cq), sp == sq)
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self.assertEqual(cp.issubset(cq), sp.issubset(sq))
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self.assertEqual(cp.issuperset(cq), sp.issuperset(sq))
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self.assertEqual(cp.isdisjoint(cq), sp.isdisjoint(sq))
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self.assertEqual(cp == cq, sp == sq)
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self.assertEqual(cp != cq, sp != sq)
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self.assertEqual(cp <= cq, sp <= sq)
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self.assertEqual(cp >= cq, sp >= sq)
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self.assertEqual(cp < cq, sp < sq)
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self.assertEqual(cp > cq, sp > sq)
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def test_multiset_equal(self):
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self.assertTrue(Counter(a=3, b=2, c=0).isequal('ababa'))
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self.assertFalse(Counter(a=3, b=2).isequal('babab'))
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def test_eq(self):
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self.assertEqual(Counter(a=3, b=2, c=0), Counter('ababa'))
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self.assertNotEqual(Counter(a=3, b=2), Counter('babab'))
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def test_multiset_subset(self):
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self.assertTrue(Counter(a=3, b=2, c=0).issubset('ababa'))
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self.assertFalse(Counter(a=3, b=2).issubset('babab'))
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def test_le(self):
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self.assertTrue(Counter(a=3, b=2, c=0) <= Counter('ababa'))
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self.assertFalse(Counter(a=3, b=2) <= Counter('babab'))
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def test_multiset_superset(self):
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self.assertTrue(Counter(a=3, b=2, c=0).issuperset('aab'))
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self.assertFalse(Counter(a=3, b=2, c=0).issuperset('aabd'))
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def test_lt(self):
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self.assertTrue(Counter(a=3, b=1, c=0) < Counter('ababa'))
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self.assertFalse(Counter(a=3, b=2, c=0) < Counter('ababa'))
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def test_multiset_disjoint(self):
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self.assertTrue(Counter(a=3, b=2, c=0).isdisjoint('cde'))
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self.assertFalse(Counter(a=3, b=2, c=0).isdisjoint('bcd'))
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def test_ge(self):
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self.assertTrue(Counter(a=2, b=1, c=0) >= Counter('aab'))
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self.assertFalse(Counter(a=3, b=2, c=0) >= Counter('aabd'))
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def test_multiset_predicates_with_negative_counts(self):
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# Multiset predicates run on the output of the elements() method,
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# meaning that zero counts and negative counts are ignored.
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# The tests below confirm that we get that same results as the
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# tests above, even after a negative count has been included
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# in either *self* or *other*.
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self.assertTrue(Counter(a=3, b=2, c=0, d=-1).isequal('ababa'))
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self.assertFalse(Counter(a=3, b=2, d=-1).isequal('babab'))
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self.assertTrue(Counter(a=3, b=2, c=0, d=-1).issubset('ababa'))
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self.assertFalse(Counter(a=3, b=2, d=-1).issubset('babab'))
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self.assertTrue(Counter(a=3, b=2, c=0, d=-1).issuperset('aab'))
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self.assertFalse(Counter(a=3, b=2, c=0, d=-1).issuperset('aabd'))
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self.assertTrue(Counter(a=3, b=2, c=0, d=-1).isdisjoint('cde'))
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self.assertFalse(Counter(a=3, b=2, c=0, d=-1).isdisjoint('bcd'))
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self.assertTrue(Counter(a=3, b=2, c=0, d=-1).isequal(Counter(a=3, b=2, c=-1)))
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self.assertFalse(Counter(a=3, b=2, d=-1).isequal(Counter(a=2, b=3, c=-1)))
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self.assertTrue(Counter(a=3, b=2, c=0, d=-1).issubset(Counter(a=3, b=2, c=-1)))
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self.assertFalse(Counter(a=3, b=2, d=-1).issubset(Counter(a=2, b=3, c=-1)))
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self.assertTrue(Counter(a=3, b=2, c=0, d=-1).issuperset(Counter(a=2, b=1, c=-1)))
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self.assertFalse(Counter(a=3, b=2, c=0, d=-1).issuperset(Counter(a=2, b=1, c=-1, d=1)))
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self.assertTrue(Counter(a=3, b=2, c=0, d=-1).isdisjoint(Counter(c=1, d=2, e=3, f=-1)))
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self.assertFalse(Counter(a=3, b=2, c=0, d=-1).isdisjoint(Counter(b=1, c=1, d=1, e=-1)))
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def test_gt(self):
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self.assertTrue(Counter(a=3, b=2, c=0) > Counter('aab'))
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self.assertFalse(Counter(a=2, b=1, c=0) > Counter('aab'))
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################################################################################
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@ -1,2 +0,0 @@
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Add multiset comparison methods to collections.Counter(): isequal(),
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issubset(), issuperset(), and isdisjoint().
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@ -0,0 +1 @@
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Add rich comparisons to collections.Counter().
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