From 4a9e2ecd87738236f9ac95561f4072e16f5c607a Mon Sep 17 00:00:00 2001
From: Uday Patel <uday3patel@gmail.com>
Date: Wed, 21 Jan 2026 15:52:55 -0500
Subject: [PATCH] feat: optimize collections.Counter.most_common() when n == 1;
 add tests for coverage; add NEWS file

---
 Lib/collections/__init__.py                    |  7 +++++++
 Lib/test/test_collections.py                   | 18 ++++++++++++++++++
 ...6-01-21-15-46-53.gh-issue-144127.aBc123.rst |  3 +++
 3 files changed, 28 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2026-01-21-15-46-53.gh-issue-144127.aBc123.rst

diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index 55ffc36ea5b0c7..21459337ca18b3 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -634,6 +634,13 @@ def most_common(self, n=None):
         if n is None:
             return sorted(self.items(), key=_itemgetter(1), reverse=True)
 
+        if n == 1:
+            # Optimization: use max() instead of heapq for single element
+            # max() raises ValueError on empty sequence, so check first
+            if not self:
+                return []
+            return [max(self.items(), key=_itemgetter(1))]
+
         # Lazy import to speedup Python startup time
         global heapq
         if heapq is None:
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index b1b2dd2ca5ca0d..935edf58a29025 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -2279,6 +2279,24 @@ def test_invariant_for_the_in_operator(self):
             self.assertTrue(elem in c)
             self.assertIn(elem, c)
 
+    def test_most_common(self):
+        c = Counter(a=5, b=3, c=5, d=2, e=0, f=-1)
+
+        self.assertEqual(c.most_common(), [('a', 5), ('c', 5), ('b', 3), ('d', 2), ('e', 0), ('f', -1)])
+        self.assertEqual(c.most_common(3), [('a', 5), ('c', 5), ('b', 3)])
+        self.assertEqual(c.most_common(0), [])
+        self.assertEqual(c.most_common(-2), [])
+        self.assertEqual(c.most_common(1), [('a', 5)])
+
+        # Test empty counter
+        empty_c = Counter()
+
+        self.assertEqual(empty_c.most_common(), [])
+        self.assertEqual(empty_c.most_common(3), [])
+        self.assertEqual(empty_c.most_common(0), [])
+        self.assertEqual(empty_c.most_common(-2), [])
+        self.assertEqual(empty_c.most_common(1), [])
+
     def test_multiset_operations(self):
         # Verify that adding a zero counter will strip zeros and negatives
         c = Counter(a=10, b=-2, c=0) + Counter()
diff --git a/Misc/NEWS.d/next/Library/2026-01-21-15-46-53.gh-issue-144127.aBc123.rst b/Misc/NEWS.d/next/Library/2026-01-21-15-46-53.gh-issue-144127.aBc123.rst
new file mode 100644
index 00000000000000..def589674c2bdd
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-01-21-15-46-53.gh-issue-144127.aBc123.rst
@@ -0,0 +1,3 @@
+Optimize :meth:`collections.Counter.most_common` for ``n=1`` to use
+:func:`max` instead of :func:`heapq.nlargest`, improving performance for
+the common case of finding the single most common element.