gh-154359: Optimize UserList type checks to use list directly

Doc/library/secrets.rst

@@ -137,7 +137,7 @@ Other functions
    :term:`bytes-like objects <bytes-like object>`
    *a* and *b* are equal, otherwise ``False``,
    using a "constant-time compare" to reduce the risk of
-   `timing attacks <https://codahale.com/a-lesson-in-timing-attacks/>`_.
+   `timing attacks <https://web.archive.org/web/20250815071532/https://codahale.com/a-lesson-in-timing-attacks/>`__.
    See :func:`hmac.compare_digest` for additional details.
 
 

Lib/collections/__init__.py

@@ -1286,7 +1286,7 @@ def __init__(self, initlist=None):
         self.data = []
         if initlist is not None:
             # XXX should this accept an arbitrary sequence?
-            if type(initlist) == type(self.data):
+            if type(initlist) is list:
                 self.data[:] = initlist
             elif isinstance(initlist, UserList):
                 self.data[:] = initlist.data[:]
@@ -1335,21 +1335,21 @@ def __delitem__(self, i):
     def __add__(self, other):
         if isinstance(other, UserList):
             return self.__class__(self.data + other.data)
-        elif isinstance(other, type(self.data)):
+        elif isinstance(other, list):
             return self.__class__(self.data + other)
         return self.__class__(self.data + list(other))
 
     def __radd__(self, other):
         if isinstance(other, UserList):
             return self.__class__(other.data + self.data)
-        elif isinstance(other, type(self.data)):
+        elif isinstance(other, list):
             return self.__class__(other + self.data)
         return self.__class__(list(other) + self.data)
 
     def __iadd__(self, other):
         if isinstance(other, UserList):
             self.data += other.data
-        elif isinstance(other, type(self.data)):
+        elif isinstance(other, list):
             self.data += other
         else:
             self.data += list(other)

Misc/NEWS.d/next/Library/2026-07-21-13-33-00.gh-issue-154359.rst

@@ -0,0 +1 @@
+Optimize the type checks in :class:`collections.UserList` to use the :class:`list` type directly instead of ``type(self.data)``.