@@ -938,34 +938,36 @@ Tests are in ``tests/unit/test_c_seqobject.py`` which includes failure modes:
938938Implementation
939939--------------
940940
941+ .. warning ::
942+ 943+ There is an undocumented feature when using `sq_ass_item ` from `PyObject_SetItem() `_ and `PyObject_DelItem() `_
944+ when using negative indexes when the negative index is *out of range *.
945+ In this case, before the `sq_ass_item ` function is called the index will have had the sequence length added to it.
946+ 947+ For example if the sequence length is 3 and the given index is -4 then the index that the `sq_ass_item ` function
948+ receives is -1.
949+ If the given index is -5 then the index that the `sq_ass_item ` function receives is -2.
950+ 951+ Thus the slightly odd code below to fix this problem.
952+ Failing to do this will mean out of range errors will not be detected by the `sq_ass_item ` function.
953+ 954+ 941955In ``src/cpy/Object/cSeqObject.c ``:
942956
943957.. code-block :: c
944958
945959 static int
946960 SequenceLongObject_sq_ass_item(PyObject *self, Py_ssize_t index, PyObject *value) {
947- fprintf(
948- stdout, "%s()#%d: self=%p index=%zd value=%p\n",
949- __FUNCTION__, __LINE__, (void *) self, index, (void *) value
950- );
951- /* This is very weird. */
961+ /* See warning above. */
952962 if (index < 0) {
953- fprintf(
954- stdout, "%s()#%d: Fixing index index=%zd to %zd\n", __FUNCTION__, __LINE__,
955- index, index - SequenceLongObject_sq_length(self)
956- );
957963 index -= SequenceLongObject_sq_length(self);
958964 }
959- /* Isn't it? */
965+
960966 Py_ssize_t my_index = index;
961967 if (my_index < 0) {
962968 my_index += SequenceLongObject_sq_length(self);
963969 }
964970 // Corner case example: len(self) == 0 and index < 0
965- fprintf(
966- stdout, "%s()#%d: len=%zd index=%zd my_index=%zd\n", __FUNCTION__, __LINE__,
967- SequenceLongObject_sq_length(self), index, my_index
968- );
969971 if (my_index < 0 || my_index >= SequenceLongObject_sq_length(self)) {
970972 PyErr_Format(
971973 PyExc_IndexError,
@@ -992,13 +994,11 @@ In ``src/cpy/Object/cSeqObject.c``:
992994 SequenceLongObject *self_as_slo = (SequenceLongObject *) self;
993995 /* Special case: deleting the only item in the array. */
994996 if (self_as_slo->size == 1) {
995- fprintf(stdout, "%s()#%d: deleting empty index\n", __FUNCTION__, __LINE__);
996997 free(self_as_slo->array_long);
997998 self_as_slo->array_long = NULL;
998999 self_as_slo->size = 0;
9991000 } else {
10001001 /* Delete the value and re-compose the array. */
1001- fprintf(stdout, "%s()#%d: deleting index=%zd\n", __FUNCTION__, __LINE__, index);
10021002 long *new_array = malloc((self_as_slo->size - 1) * sizeof(long));
10031003 if (!new_array) {
10041004 PyErr_Format(
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