str: Initial implementation of string slicing.

Only step=1 and non-negative indexes are supported so far.

1 files changed, 15 insertions, 1 deletions

diff --git a/py/objstr.c b/py/objstr.c
index 48abf4951d..46adabcec9 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -29,7 +29,21 @@ mp_obj_t str_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
         case RT_BINARY_OP_SUBSCR:
             // string access
             // XXX a massive hack!
-            return mp_obj_new_int(lhs_str[mp_obj_get_int(rhs_in)]);
+
+            // TODO: need predicate to check for int-like type (bools are such for example)
+            // ["no", "yes"][1 == 2] is common idiom
+            if (MP_OBJ_IS_SMALL_INT(rhs_in)) {
+                // TODO: This implements byte string access for single index so far
+                return mp_obj_new_int(lhs_str[mp_obj_get_int(rhs_in)]);
+            } else if (MP_OBJ_IS_TYPE(rhs_in, &slice_type)) {
+                int start, stop, step;
+                mp_obj_slice_get(rhs_in, &start, &stop, &step);
+                assert(step == 1);
+                return mp_obj_new_str(qstr_from_strn_copy(lhs_str + start, stop - start));
+            } else {
+                // Throw TypeError here
+                assert(0);
+            }
 
         case RT_BINARY_OP_ADD:
         case RT_BINARY_OP_INPLACE_ADD: