https://github.com/python/cpython/commit/d14e31ed683886bde240006cb2e2fd78303e6518
commit: d14e31ed683886bde240006cb2e2fd78303e6518
branch: main
author: Anerdw <[email protected]>
committer: rhettinger <[email protected]>
date: 2026-04-14T23:29:41-05:00
summary:
gh-147957: pop items from UserDict in LIFO order (gh-147958)
files:
A Misc/NEWS.d/next/Library/2026-04-01-07-10-49.gh-issue-147957.QXf5Xx.rst
M Doc/library/collections.rst
M Lib/collections/__init__.py
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index c8dcaef80188cd..cb9300f072b9e7 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -1346,7 +1346,14 @@ attribute.
A real dictionary used to store the contents of the :class:`UserDict`
class.
+ :class:`!UserDict` instances also override the following method:
+ .. method:: popitem
+
+ Remove and return a ``(key, value)`` pair from the wrapped dictionary.
Pairs are
+ returned in the same order as ``data.popitem()``. (For the default
+ :meth:`dict.popitem`, this order is :abbr:`LIFO (last-in,
first-out)`.) If the
+ dictionary is empty, raises a :exc:`KeyError`.
:class:`UserList` objects
-------------------------
diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index febab521629228..20f1e728733fec 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -1253,6 +1253,20 @@ def copy(self):
c.update(self)
return c
+
+ # This method has a default implementation in MutableMapping, but dict's
+ # equivalent is last-in, first-out instead of first-in, first-out.
+ def popitem(self):
+ """Remove and return a (key, value) pair as a 2-tuple.
+
+ Removes pairs in the same order as the wrapped mapping's popitem()
+ method. For dict objects (the default), that order is last-in,
+ first-out (LIFO).
+ Raises KeyError if the UserDict is empty.
+ """
+ return self.data.popitem()
+
+
@classmethod
def fromkeys(cls, iterable, value=None):
d = cls()
diff --git
a/Misc/NEWS.d/next/Library/2026-04-01-07-10-49.gh-issue-147957.QXf5Xx.rst
b/Misc/NEWS.d/next/Library/2026-04-01-07-10-49.gh-issue-147957.QXf5Xx.rst
new file mode 100644
index 00000000000000..4a0e15d01c72b6
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-04-01-07-10-49.gh-issue-147957.QXf5Xx.rst
@@ -0,0 +1 @@
+Guarantees that :meth:`collections.UserDict.popitem` will pop in the same
order as the wrapped dictionary rather than an arbitrary order.
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