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bpo-36650: Fix handling of empty keyword args in C version of lru_cache. (GH-12881)

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Raymond Hettinger 2019-04-20 07:20:44 -10:00 committed by GitHub
parent 9d062d690b
commit 14adbd4598
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3 changed files with 21 additions and 4 deletions
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14
Lib/test/test_functools.py
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@ -1271,6 +1271,20 @@ class TestLRU:
self.assertEqual(f(20), '.20.')
self.assertEqual(f.cache_info().currsize, 10)
def test_lru_bug_36650(self):
# C version of lru_cache was treating a call with an empty **kwargs
# dictionary as being distinct from a call with no keywords at all.
# This did not result in an incorrect answer, but it did trigger
# an unexpected cache miss.
@self.module.lru_cache()
def f(x):
pass
f(0)
f(0, **{})
self.assertEqual(f.cache_info().hits, 1)
def test_lru_hash_only_once(self):
# To protect against weird reentrancy bugs and to improve
# efficiency when faced with slow __hash__ methods, the

4
Misc/NEWS.d/next/Library/2019-04-19-15-29-55.bpo-36650._EVdrz.rst Normal file
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@ -0,0 +1,4 @@
The C version of functools.lru_cache() was treating calls with an empty
``**kwargs`` dictionary as being distinct from calls with no keywords at all.
This did not result in an incorrect answer, but it did trigger an unexpected
cache miss.

7
Modules/_functoolsmodule.c
View File

@ -750,8 +750,10 @@ lru_cache_make_key(PyObject *args, PyObject *kwds, int typed)
PyObject *key, *keyword, *value;
Py_ssize_t key_size, pos, key_pos, kwds_size;
kwds_size = kwds ? PyDict_GET_SIZE(kwds) : 0;
/* short path, key will match args anyway, which is a tuple */
if (!typed && !kwds) {
if (!typed && !kwds_size) {
if (PyTuple_GET_SIZE(args) == 1) {
key = PyTuple_GET_ITEM(args, 0);
if (PyUnicode_CheckExact(key) || PyLong_CheckExact(key)) {
@ -765,9 +767,6 @@ lru_cache_make_key(PyObject *args, PyObject *kwds, int typed)
return args;
}
kwds_size = kwds ? PyDict_GET_SIZE(kwds) : 0;
assert(kwds_size >= 0);
key_size = PyTuple_GET_SIZE(args);
if (kwds_size)
key_size += kwds_size * 2 + 1;