py: Fix mult by negative number of tuple, list, str, bytes.

Multiplication of a tuple, list, str or bytes now yields an empty
sequence (instead of crashing).  Addresses issue #799

Also added ability to mult bytes on LHS by integer.

py/objint.c

@@ -289,7 +289,7 @@ mp_obj_t mp_obj_int_binary_op_extra_cases(int op, mp_obj_t lhs_in, mp_obj_t rhs_
         // true acts as 0
         return mp_binary_op(op, lhs_in, MP_OBJ_NEW_SMALL_INT(1));
     } else if (op == MP_BINARY_OP_MULTIPLY) {
-        if (MP_OBJ_IS_STR(rhs_in) || MP_OBJ_IS_TYPE(rhs_in, &mp_type_tuple) || MP_OBJ_IS_TYPE(rhs_in, &mp_type_list)) {
+        if (MP_OBJ_IS_STR(rhs_in) || MP_OBJ_IS_TYPE(rhs_in, &mp_type_bytes) || MP_OBJ_IS_TYPE(rhs_in, &mp_type_tuple) || MP_OBJ_IS_TYPE(rhs_in, &mp_type_list)) {
             // multiply is commutative for these types, so delegate to them
             return mp_binary_op(op, rhs_in, lhs_in);
         }

py/objlist.c

@@ -131,6 +131,9 @@ STATIC mp_obj_t list_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
             if (!mp_obj_get_int_maybe(rhs, &n)) {
                 return MP_OBJ_NULL; // op not supported
             }
+            if (n < 0) {
+                n = 0;
+            }
             mp_obj_list_t *s = list_new(o->len * n);
             mp_seq_multiply(o->items, sizeof(*o->items), o->len, n, s->items);
             return s;

py/objstr.c

@@ -290,10 +290,16 @@ mp_obj_t mp_obj_str_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
             break;
 
         case MP_BINARY_OP_MULTIPLY: {
-            if (!MP_OBJ_IS_SMALL_INT(rhs_in)) {
+            mp_int_t n;
+            if (!mp_obj_get_int_maybe(rhs_in, &n)) {
                 return MP_OBJ_NULL; // op not supported
             }
-            int n = MP_OBJ_SMALL_INT_VALUE(rhs_in);
+            if (n <= 0) {
+                if (lhs_type == &mp_type_str) {
+                    return MP_OBJ_NEW_QSTR(MP_QSTR_); // empty str
+                }
+                n = 0;
+            }
             byte *data;
             mp_obj_t s = mp_obj_str_builder_start(lhs_type, lhs_len * n, &data);
             mp_seq_multiply(lhs_data, sizeof(*lhs_data), lhs_len, n, data);

py/objtuple.c

@@ -137,10 +137,13 @@ mp_obj_t mp_obj_tuple_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
             return s;
         }
         case MP_BINARY_OP_MULTIPLY: {
-            if (!MP_OBJ_IS_SMALL_INT(rhs)) {
+            mp_int_t n;
+            if (!mp_obj_get_int_maybe(rhs, &n)) {
                 return MP_OBJ_NULL; // op not supported
             }
-            int n = MP_OBJ_SMALL_INT_VALUE(rhs);
+            if (n <= 0) {
+                return mp_const_empty_tuple;
+            }
             mp_obj_tuple_t *s = mp_obj_new_tuple(o->len * n, NULL);
             mp_seq_multiply(o->items, sizeof(*o->items), o->len, n, s->items);
             return s;

tests/basics/bytes_mult.py

@@ -0,0 +1,12 @@
+# basic multiplication
+print(b'0' * 5)
+
+# check negative, 0, positive; lhs and rhs multiplication
+for i in (-4, -2, 0, 2, 4):
+    print(i * b'12')
+    print(b'12' * i)
+
+# check that we don't modify existing object
+a = b'123'
+c = a * 3
+print(a, c)

tests/basics/list_mult.py

@@ -1,4 +1,12 @@
+# basic multiplication
 print([0] * 5)
+
+# check negative, 0, positive; lhs and rhs multiplication
+for i in (-4, -2, 0, 2, 4):
+    print(i * [1, 2])
+    print([1, 2] * i)
+
+# check that we don't modify existing list
 a = [1, 2, 3]
 c = a * 3
-print(c)
+print(a, c)

tests/basics/string_mult.py

@@ -0,0 +1,12 @@
+# basic multiplication
+print('0' * 5)
+
+# check negative, 0, positive; lhs and rhs multiplication
+for i in (-4, -2, 0, 2, 4):
+    print(i * '12')
+    print('12' * i)
+
+# check that we don't modify existing object
+a = '123'
+c = a * 3
+print(a, c)

tests/basics/tuple_mult.py

@@ -1,4 +1,12 @@
+# basic multiplication
 print((0,) * 5)
+
+# check negative, 0, positive; lhs and rhs multiplication
+for i in (-4, -2, 0, 2, 4):
+    print(i * (1, 2))
+    print((1, 2) * i)
+
+# check that we don't modify existing tuple
 a = (1, 2, 3)
 c = a * 3
-print(c)
+print(a, c)