New submission from Ma Lin <malin...@163.com>: PyBytes_FromStringAndSize() uses a global cache for 1-byte bytes: https://github.com/python/cpython/blob/v3.10.0a4/Objects/bytesobject.c#L147
if (size == 1 && str != NULL) { struct _Py_bytes_state *state = get_bytes_state(); op = state->characters[*str & UCHAR_MAX]; if (op != NULL) { Py_INCREF(op); return (PyObject *)op; } } _PyBytes_Resize() will raise an error when (refcount != 1): https://github.com/python/cpython/blob/v3.10.0a4/Objects/bytesobject.c#L3029 Then this code will raise an exception: obj1 = PyBytes_FromStringAndSize("a", 1); obj2 = PyBytes_FromStringAndSize("a", 1); ret = _PyBytes_Resize(&obj2, 2); // ret is -1 BTW, 0-byte bytes comes from a global singleton, but _PyBytes_Resize() processes it before checking refcount: https://github.com/python/cpython/blob/v3.10.0a4/Objects/bytesobject.c#L3021 if (Py_SIZE(v) == 0) { if (newsize == 0) { return 0; } *pv = _PyBytes_FromSize(newsize, 0); Py_DECREF(v); return (*pv == NULL) ? -1 : 0; } if (Py_REFCNT(v) != 1) { goto error; } _PyBytes_Resize() doc: Only use this to build up a brand new bytes object; don’t use this if the bytes may already be known in other parts of the code. It is an error to call this function if the refcount on the input bytes object is not one. ---------- components: Interpreter Core messages: 385689 nosy: malin priority: normal severity: normal status: open title: Calling _PyBytes_Resize() on 1-byte bytes may raise error type: behavior versions: Python 3.10, Python 3.8, Python 3.9 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue43027> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com