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slice: Implement special handling of omitted start/stop indexes.

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This commit is contained in:
Paul Sokolovsky 2014-01-03 23:35:32 +02:00
parent cd22627f78
commit 59800afae9
1 changed files with 17 additions and 2 deletions
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19
py/objslice.c
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@ -39,8 +39,23 @@ const mp_obj_type_t slice_type = {
// TODO: Make sure to handle "empty" values, which are signified by None in CPython
mp_obj_t mp_obj_new_slice(mp_obj_t ostart, mp_obj_t ostop, mp_obj_t ostep) {
assert(ostep == NULL);
machine_int_t start = mp_obj_get_int(ostart);
machine_int_t stop = mp_obj_get_int(ostop);
machine_int_t start = 0, stop = 0;
if (ostart != mp_const_none) {
start = mp_obj_get_int(ostart);
}
if (ostop != mp_const_none) {
stop = mp_obj_get_int(ostop);
if (stop == 0) {
// [x:0] is a special case - in our slice object, stop = 0 means
// "end of sequence". Fortunately, [x:0] is an empty seqence for
// any x (including negative). [x:x] is also always empty sequence.
// but x also can be 0. But note that b""[x:x] is b"" for any x (i.e.
// no IndexError, at least in Python 3.3.3). So, we just use -1's to
// signify that. -1 is catchy "special" number in case someone will
// try to print [x:0] slice ever.
start = stop = -1;
}
}
mp_obj_slice_t *o = m_new(mp_obj_slice_t, 1);
o->base.type = &slice_type;
o->start = start;