py: Implement iterator support for object that has __getitem__.

Addresses Issue #203.

1 files changed, 53 insertions, 0 deletions

diff --git a/py/objgetitemiter.c b/py/objgetitemiter.c
new file mode 100644
index 000000000..40ed1a152
--- /dev/null
+++ b/py/objgetitemiter.c
@@ -0,0 +1,53 @@
+#include <stdlib.h>
+#include <stdint.h>
+
+#include "nlr.h"
+#include "misc.h"
+#include "mpconfig.h"
+#include "qstr.h"
+#include "obj.h"
+#include "runtime.h"
+
+// this is a wrapper object that is turns something that has a __getitem__ method into an iterator
+
+typedef struct _mp_obj_getitem_iter_t {
+    mp_obj_base_t base;
+    mp_obj_t args[3];
+} mp_obj_getitem_iter_t;
+
+static mp_obj_t it_iternext(mp_obj_t self_in) {
+    mp_obj_getitem_iter_t *self = self_in;
+    nlr_buf_t nlr;
+    if (nlr_push(&nlr) == 0) {
+        // try to get next item
+        mp_obj_t value = rt_call_method_n_kw(1, 0, self->args);
+        self->args[2] = MP_OBJ_NEW_SMALL_INT(MP_OBJ_SMALL_INT_VALUE(self->args[2]) + 1);
+        nlr_pop();
+        return value;
+    } else {
+        // an exception was raised
+        if (MP_OBJ_IS_TYPE(nlr.ret_val, &exception_type) && mp_obj_exception_get_type(nlr.ret_val) == MP_QSTR_StopIteration) {
+            // return mp_const_stop_iteration instead of raising StopIteration
+            return mp_const_stop_iteration;
+        } else {
+            // re-raise exception
+            nlr_jump(nlr.ret_val);
+        }
+    }
+}
+
+static const mp_obj_type_t it_type = {
+    { &mp_const_type },
+    "iterator",
+    .iternext = it_iternext
+};
+
+// args are those returned from rt_load_method_maybe (ie either an attribute or a method)
+mp_obj_t mp_obj_new_getitem_iter(mp_obj_t *args) {
+    mp_obj_getitem_iter_t *o = m_new_obj(mp_obj_getitem_iter_t);
+    o->base.type = &it_type;
+    o->args[0] = args[0];
+    o->args[1] = args[1];
+    o->args[2] = MP_OBJ_NEW_SMALL_INT(0);
+    return o;
+}