Raymond Hettinger <raymond.hettin...@gmail.com> added the comment:
For the record, here's what is going on. The method_cache() code uses a slightly different invocation for the first call than for subsequent calls. In particular, the wrapper() uses **kwargs with an empty dict whereas the first call didn't use keyword arguments at all. The C version of the lru_cache() is treating that first call as distinct from the second call, resulting in a cache miss for the both the first and second invocation but not in subsequent invocations. The pure python lru_cache() has a memory saving fast path taken when kwds is an empty dict. The C version is out-of-sync with because it runs the that path only when kwds==NULL and it doesn't check for the case where kwds is an empty dict. Here's a minimal reproducer: @lru_cache() def f(x): pass f(0) f(0, **{}) assert f.cache_info().hits == 1 Here's a possible fix: diff --git a/Modules/_functoolsmodule.c b/Modules/_functoolsmodule.c index 3f1c01651d..f118119479 100644 --- a/Modules/_functoolsmodule.c +++ b/Modules/_functoolsmodule.c @@ -751,7 +751,7 @@ lru_cache_make_key(PyObject *args, PyObject *kwds, int typed) Py_ssize_t key_size, pos, key_pos, kwds_size; /* short path, key will match args anyway, which is a tuple */ - if (!typed && !kwds) { + if (!typed && (!kwds || PyDict_GET_SIZE(kwds) == 0)) { if (PyTuple_GET_SIZE(args) == 1) { key = PyTuple_GET_ITEM(args, 0); if (PyUnicode_CheckExact(key) || PyLong_CheckExact(key)) { ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue36650> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com