py: Add support for start/stop/step attributes of builtin range object.

py/mpconfig.h

@@ -382,6 +382,12 @@ typedef double mp_float_t;
 #define MICROPY_PY_BUILTINS_PROPERTY (1)
 #endif
 
+// Whether to implement the start/stop/step attributes (readback) on
+// the "range" builtin type. Rarely used, and costs ~60 bytes (x86).
+#ifndef MICROPY_PY_BUILTINS_RANGE_ATTRS
+#define MICROPY_PY_BUILTINS_RANGE_ATTRS (1)
+#endif
+
 // Whether to support complete set of special methods
 // for user classes, otherwise only the most used
 #ifndef MICROPY_PY_ALL_SPECIAL_METHODS

py/objrange.c

@@ -166,6 +166,20 @@ STATIC mp_obj_t range_getiter(mp_obj_t o_in) {
     return mp_obj_new_range_iterator(o->start, o->stop, o->step);
 }
 
+
+#if MICROPY_PY_BUILTINS_RANGE_ATTRS
+STATIC void range_load_attr(mp_obj_t o_in, qstr attr, mp_obj_t *dest) {
+    mp_obj_range_t *o = o_in;
+    if (attr == MP_QSTR_start) {
+        dest[0] = mp_obj_new_int(o->start);
+    } else if (attr == MP_QSTR_stop) {
+        dest[0] = mp_obj_new_int(o->stop);
+    } else if (attr == MP_QSTR_step) {
+        dest[0] = mp_obj_new_int(o->step);
+    }
+}
+#endif
+
 const mp_obj_type_t mp_type_range = {
     { &mp_type_type },
     .name = MP_QSTR_range,
@@ -174,4 +188,7 @@ const mp_obj_type_t mp_type_range = {
     .unary_op = range_unary_op,
     .subscr = range_subscr,
     .getiter = range_getiter,
+#if MICROPY_PY_BUILTINS_RANGE_ATTRS
+    .load_attr = range_load_attr,
+#endif
 };

py/qstrdefs.h

@@ -245,6 +245,11 @@ Q(single)
 Q(sep)
 Q(end)
 
+#if MICROPY_PY_BUILTINS_RANGE_ATTRS
+Q(step)
+Q(stop)
+#endif
+
 Q(clear)
 Q(copy)
 Q(fromkeys)

tests/basics/builtin_range.py

@@ -24,3 +24,8 @@ print(range(4)[1:2])
 print(range(4)[1:3])
 print(range(4)[1::2])
 print(range(4)[1:-2:2])
+
+# attrs
+print(range(1, 2, 3).start)
+print(range(1, 2, 3).stop)
+print(range(1, 2, 3).step)