diff --git a/arfx/core.py b/arfx/core.py
index 4828263..741f6e7 100644
--- a/arfx/core.py
+++ b/arfx/core.py
@@ -20,6 +20,7 @@
 import logging
 import os
 import sys
+from functools import cache
 
 import arf
 import h5py as h5
@@ -367,10 +368,8 @@ def copy_entries(tgt, files, **options):
 
     from h5py import Group
 
-    from .tools import memoized
-
     ebase = options.get("template", None)
-    acache = memoized(arf.open_file)
+    acache = cache(arf.open_file)
 
     with arf.open_file(tgt, "a") as arfp:
         arf.check_file_version(arfp)
@@ -381,8 +380,8 @@ def copy_entries(tgt, files, **options):
             # on windows, dir\file.arf/entry is an entry
             pn, fn = pp.split(f)
             if os.path.isfile(f):
-                it = ((f, entry) for ename, entry in acache(f).items())
-            elif os.path.isfile(pn):
+                it = ((f, entry) for ename, entry in acache(f, mode="r").items())
+            elif os.path.isfile(pn, mode="r"):
                 fp = acache(pn)
                 if fn in fp:
                     it = ((pn, fp[fn]),)
diff --git a/arfx/tools.py b/arfx/tools.py
deleted file mode 100644
index 018dcd0..0000000
--- a/arfx/tools.py
+++ /dev/null
@@ -1,37 +0,0 @@
-# -*- coding: utf-8 -*-
-# -*- mode: python -*-
-""" General programming tools """
-import collections
-import functools
-
-
-class memoized(object):
-    """Memoizing decorator. Caches a function's return value each time it is called.
-    If called later with the same arguments, the cached value is returned
-    instead of evaluating the function.
-    """
-
-    def __init__(self, func):
-        self.func = func
-        self.cache = {}
-        functools.update_wrapper(self, func)
-
-    def __call__(self, *args):
-        if not isinstance(args, collections.Hashable):
-            # uncacheable. a list, for instance.
-            # better to not cache than blow up.
-            return self.func(*args)
-        if args in self.cache:
-            return self.cache[args]
-        else:
-            value = self.func(*args)
-            self.cache[args] = value
-            return value
-
-    def __repr__(self):
-        """Return the function's docstring."""
-        return self.func.__doc__
-
-    def __get__(self, obj, objtype):
-        """Support instance methods."""
-        return functools.partial(self.__call__, obj)
diff --git a/uv.lock b/uv.lock
index 7e0bde2..fd09169 100644
--- a/uv.lock
+++ b/uv.lock
@@ -27,7 +27,7 @@ wheels = [
 
 [[package]]
 name = "arfx"
-version = "2.7.0"
+version = "2.7.1"
 source = { editable = "." }
 dependencies = [
     { name = "arf" },