gh-154746: Update docstring for `collections.Counter` (GH-154792)

https://github.com/python/cpython/commit/22a123f1305bf45d5d35441e9164fb4528da493c
commit: 22a123f1305bf45d5d35441e9164fb4528da493c
branch: main
author: Dan Shernicoff <[email protected]>
committer: ZeroIntensity <[email protected]>
date: 2026-07-28T01:41:17Z
summary:

gh-154746: Update docstring for `collections.Counter` (GH-154792)

Added a note to `collections.Counter`'s docstring that initializing a `Counter` from a `Mapping` or `Counter` will have different behaviour than initializing from other `Iterable`s.

This behaviour was already documented in the canonical docs but is missing from the help() output.

files:
M Lib/collections/__init__.py

diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index 20f1e728733fec6..5dbcac19e7a9272 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -553,6 +553,9 @@ class Counter(dict):
     or multiset.  Elements are stored as dictionary keys and their counts
     are stored as dictionary values.
 
+    When constructed from a Mapping or Counter, the original object's
+    values will be used as the initial counts.
+
     >>> c = Counter('abcdeabcdabcaba')  # count elements from a string
 
     >>> c.most_common(3)                # three most common elements

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