From 139dc7cb594b9517b2735e1f66909bb41445e4e5 Mon Sep 17 00:00:00 2001
From: James Cave <jcave137@gmail.com>
Date: Sat, 22 Jul 2023 21:58:09 -0400
Subject: [PATCH] gh-107089: Improve Shelf.clear method performance

The clear method used to be implemented by inheriting a mix-in from the
MutableMapping ABC. It was a poor fit for shelves, and a better
implementation is now in place
---
 Lib/shelve.py                                 | 19 +++++++++++++++++++
 Misc/ACKS                                     |  1 +
 ...-07-22-21-57-34.gh-issue-107089.Dnget2.rst |  2 ++
 3 files changed, 22 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2023-07-22-21-57-34.gh-issue-107089.Dnget2.rst

diff --git a/Lib/shelve.py b/Lib/shelve.py
index e053c397345a07e..fd908bc23fe0ade 100644
--- a/Lib/shelve.py
+++ b/Lib/shelve.py
@@ -171,6 +171,25 @@ def sync(self):
         if hasattr(self.dict, 'sync'):
             self.dict.sync()
 
+    def clear(self):
+        """Remove all items from the shelf."""
+        self.cache.clear()
+        try:
+            self.dict.clear()
+        except AttributeError:
+            # dbm objects don't have a clear method, so we need to do
+            # the clearing here.
+            keys = self.dict.keys()
+            if not isinstance(keys, list):
+                # The keys method on dbm objects returns a list.
+                # Typically, the keys method on a mapping returns a
+                # lazy iterator, so we need to watch out for that in
+                # case someone passes in a backing object that behaves
+                # that way.
+                keys = list(keys)
+            for k in keys:
+                del self.dict[k]
+
 
 class BsdDbShelf(Shelf):
     """Shelf implementation using the "BSD" db interface.
diff --git a/Misc/ACKS b/Misc/ACKS
index fadf488888aa8ba..8b8c5ad8434bd72 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -289,6 +289,7 @@ Edward Catmur
 Lorenzo M. Catucci
 Bruno Cauet
 Donn Cave
+James Cave
 Charles Cazabon
 Jesús Cea Avión
 Per Cederqvist
diff --git a/Misc/NEWS.d/next/Library/2023-07-22-21-57-34.gh-issue-107089.Dnget2.rst b/Misc/NEWS.d/next/Library/2023-07-22-21-57-34.gh-issue-107089.Dnget2.rst
new file mode 100644
index 000000000000000..c67301a918ae600
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-07-22-21-57-34.gh-issue-107089.Dnget2.rst
@@ -0,0 +1,2 @@
+The :meth:`Shelf.clear` method in the :mod:`shelve` module is much faster.
+Patch by James Cave.