[Python-checkins] cpython (merge 3.6 -> default): merge

Fri Dec 16 17:01:26 EST 2016

https://hg.python.org/cpython/rev/c6346144a9bb
changeset: 105690:c6346144a9bb
parent: 105687:b51914417b41
parent: 105689:b3d27b5f2d23
user: Raymond Hettinger <python at rcn.com>
date: Fri Dec 16 13:59:57 2016 -0800
summary:
 merge
files:
 Lib/functools.py | 6 ++++--
 Lib/test/test_functools.py | 13 +++++++++++++
 Misc/NEWS | 3 +++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/Lib/functools.py b/Lib/functools.py
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -574,14 +574,16 @@
 last = root[PREV]
 link = [last, root, key, result]
 last[NEXT] = root[PREV] = cache[key] = link
- full = (len(cache) >= maxsize)
+ # Use the __len__() method instead of the len() function
+ # which could potentially be wrapped in an lru_cache itself.
+ full = (cache.__len__() >= maxsize)
 misses += 1
 return result
 
 def cache_info():
 """Report cache statistics"""
 with lock:
- return _CacheInfo(hits, misses, maxsize, len(cache))
+ return _CacheInfo(hits, misses, maxsize, cache.__len__())
 
 def cache_clear():
 """Clear the cache and cache statistics"""
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -1,4 +1,5 @@
 import abc
+import builtins
 import collections
 import copy
 from itertools import permutations
@@ -1189,6 +1190,18 @@
 self.assertEqual(misses, 4)
 self.assertEqual(currsize, 2)
 
+ def test_lru_reentrancy_with_len(self):
+ # Test to make sure the LRU cache code isn't thrown-off by
+ # caching the built-in len() function. Since len() can be
+ # cached, we shouldn't use it inside the lru code itself.
+ old_len = builtins.len
+ try:
+ builtins.len = self.module.lru_cache(4)(len)
+ for i in [0, 0, 1, 2, 3, 3, 4, 5, 6, 1, 7, 2, 1]:
+ self.assertEqual(len('abcdefghijklmn'[:i]), i)
+ finally:
+ builtins.len = old_len
+
 def test_lru_type_error(self):
 # Regression test for issue #28653.
 # lru_cache was leaking when one of the arguments
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -17,6 +17,9 @@
 to/from UTF-8, instead of the locale encoding to avoid inconsistencies with
 os.fsencode() and os.fsdecode() which are already using UTF-8.
 
+- Issue #28991: functools.lru_cache() was susceptible to an obscure $
+ bug triggerable by a monkey-patched len() function.
+
 - Issue #28147: Fix a memory leak in split-table dictionaries: setattr()
 must not convert combined table into split table. Patch written by INADA
 Naoki.
-- 
Repository URL: https://hg.python.org/cpython
