py: Implement builtin reversed() function.

reversed function now implemented, and works for tuple, list, str, bytes
and user objects with __len__ and __getitem__.

Renamed mp_builtin_len to mp_obj_len to make it publically available (eg
for reversed).

py/builtin.c

@@ -284,17 +284,6 @@ STATIC mp_obj_t mp_builtin_iter(mp_obj_t o_in) {
 
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_iter_obj, mp_builtin_iter);
 
-STATIC mp_obj_t mp_builtin_len(mp_obj_t o_in) {
-    mp_obj_t len = mp_obj_len_maybe(o_in);
-    if (len == MP_OBJ_NULL) {
-        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_TypeError, "object of type '%s' has no len()", mp_obj_get_type_str(o_in)));
-    } else {
-        return len;
-    }
-}
-
-MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_len_obj, mp_builtin_len);
-
 STATIC mp_obj_t mp_builtin_max(uint n_args, const mp_obj_t *args) {
     if (n_args == 1) {
         // given an iterable
@@ -569,6 +558,7 @@ STATIC mp_obj_t mp_builtin_hasattr(mp_obj_t object_in, mp_obj_t attr_in) {
 
 MP_DEFINE_CONST_FUN_OBJ_2(mp_builtin_hasattr_obj, mp_builtin_hasattr);
 
-// These two are defined in terms of MicroPython API functions right away
+// These are defined in terms of MicroPython API functions right away
+MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_len_obj, mp_obj_len);
 MP_DEFINE_CONST_FUN_OBJ_0(mp_builtin_globals_obj, mp_globals_get);
 MP_DEFINE_CONST_FUN_OBJ_0(mp_builtin_locals_obj, mp_locals_get);

py/builtin.h

@@ -26,6 +26,7 @@
 
 mp_obj_t mp_builtin___import__(uint n_args, mp_obj_t *args);
 mp_obj_t mp_builtin_open(uint n_args, const mp_obj_t *args);
+mp_obj_t mp_builtin_len(mp_obj_t o);
 
 MP_DECLARE_CONST_FUN_OBJ(mp_builtin___build_class___obj);
 MP_DECLARE_CONST_FUN_OBJ(mp_builtin___import___obj);

py/builtintables.c

@@ -66,6 +66,7 @@ STATIC const mp_map_elem_t mp_builtin_object_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR_property), (mp_obj_t)&mp_type_property },
 #endif
     { MP_OBJ_NEW_QSTR(MP_QSTR_range), (mp_obj_t)&mp_type_range },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_reversed), (mp_obj_t)&mp_type_reversed },
 #if MICROPY_PY_BUILTINS_SET
     { MP_OBJ_NEW_QSTR(MP_QSTR_set), (mp_obj_t)&mp_type_set },
 #endif

py/obj.c

@@ -360,6 +360,16 @@ uint mp_get_index(const mp_obj_type_t *type, mp_uint_t len, mp_obj_t index, bool
     return i;
 }
 
+// will raise a TypeError if object has no length
+mp_obj_t mp_obj_len(mp_obj_t o_in) {
+    mp_obj_t len = mp_obj_len_maybe(o_in);
+    if (len == MP_OBJ_NULL) {
+        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_TypeError, "object of type '%s' has no len()", mp_obj_get_type_str(o_in)));
+    } else {
+        return len;
+    }
+}
+
 // may return MP_OBJ_NULL
 mp_obj_t mp_obj_len_maybe(mp_obj_t o_in) {
     if (

py/obj.h

@@ -312,6 +312,7 @@ extern const mp_obj_type_t mp_type_classmethod;
 extern const mp_obj_type_t mp_type_property;
 extern const mp_obj_type_t mp_type_stringio;
 extern const mp_obj_type_t mp_type_bytesio;
+extern const mp_obj_type_t mp_type_reversed;
 
 // Exceptions
 extern const mp_obj_type_t mp_type_BaseException;
@@ -424,6 +425,7 @@ void mp_obj_get_complex(mp_obj_t self_in, mp_float_t *real, mp_float_t *imag);
 void mp_obj_get_array(mp_obj_t o, uint *len, mp_obj_t **items);
 void mp_obj_get_array_fixed_n(mp_obj_t o, uint len, mp_obj_t **items);
 uint mp_get_index(const mp_obj_type_t *type, mp_uint_t len, mp_obj_t index, bool is_slice);
+mp_obj_t mp_obj_len(mp_obj_t o_in);
 mp_obj_t mp_obj_len_maybe(mp_obj_t o_in); /* may return MP_OBJ_NULL */
 mp_obj_t mp_obj_subscr(mp_obj_t base, mp_obj_t index, mp_obj_t val);
 

py/objreversed.c

@@ -0,0 +1,74 @@
+/*
+ * This file is part of the Micro Python project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdlib.h>
+#include <assert.h>
+
+#include "mpconfig.h"
+#include "nlr.h"
+#include "misc.h"
+#include "qstr.h"
+#include "obj.h"
+#include "runtime.h"
+
+typedef struct _mp_obj_reversed_t {
+    mp_obj_base_t base;
+    mp_obj_t seq;           // sequence object that we are reversing
+    mp_uint_t cur_index;    // current index, plus 1; 0=no more, 1=last one (index 0)
+} mp_obj_reversed_t;
+
+STATIC mp_obj_t reversed_make_new(mp_obj_t type_in, uint n_args, uint n_kw, const mp_obj_t *args) {
+    mp_arg_check_num(n_args, n_kw, 1, 1, false);
+
+    mp_obj_reversed_t *o = m_new_obj(mp_obj_reversed_t);
+    o->base.type = &mp_type_reversed;
+    o->seq = args[0];
+    o->cur_index = mp_obj_get_int(mp_obj_len(args[0])); // start at the end of the sequence
+
+    return o;
+}
+
+STATIC mp_obj_t reversed_iternext(mp_obj_t self_in) {
+    assert(MP_OBJ_IS_TYPE(self_in, &mp_type_reversed));
+    mp_obj_reversed_t *self = self_in;
+
+    // "raise" stop iteration if we are at the end (the start) of the sequence
+    if (self->cur_index == 0) {
+        return MP_OBJ_STOP_ITERATION;
+    }
+
+    // pre-decrement and index sequence
+    self->cur_index -= 1;
+    return mp_obj_subscr(self->seq, MP_OBJ_NEW_SMALL_INT(self->cur_index), MP_OBJ_SENTINEL);
+}
+
+const mp_obj_type_t mp_type_reversed = {
+    { &mp_type_type },
+    .name = MP_QSTR_reversed,
+    .make_new = reversed_make_new,
+    .getiter = mp_identity,
+    .iternext = reversed_iternext,
+};

py/py.mk

@@ -72,6 +72,7 @@ PY_O_BASENAME = \
 	objnone.o \
 	objnamedtuple.o \
 	objrange.o \
+	objreversed.o \
 	objset.o \
 	objslice.o \
 	objstr.o \

py/qstrdefs.h

@@ -175,6 +175,7 @@ Q(print)
 Q(range)
 Q(read)
 Q(repr)
+Q(reversed)
 Q(set)
 Q(sorted)
 Q(staticmethod)

tests/basics/builtin_reversed.py

@@ -0,0 +1,33 @@
+# test the builtin reverse() function
+
+# list
+print(list(reversed([])))
+print(list(reversed([1])))
+print(list(reversed([1, 2, 3])))
+
+# tuple
+print(list(reversed(())))
+print(list(reversed((1, 2, 3))))
+
+# string
+for c in reversed('ab'):
+    print(c)
+
+# bytes
+for b in reversed(b'1234'):
+    print(b)
+
+# range
+#for i in reversed(range(3)):
+#    print(i)
+
+# user object
+class A:
+    def __init__(self):
+        pass
+    def __len__(self):
+        return 3
+    def __getitem__(self, pos):
+        return pos + 1
+for a in reversed(A()):
+    print(a)