diff --git a/py/builtin.h b/py/builtin.h
index 743f748da0..caca71b523 100644
--- a/py/builtin.h
+++ b/py/builtin.h
@@ -37,6 +37,8 @@ MP_DECLARE_CONST_FUN_OBJ(mp_namedtuple_obj);
 
 MP_DECLARE_CONST_FUN_OBJ(mp_op_contains_obj);
 MP_DECLARE_CONST_FUN_OBJ(mp_op_getitem_obj);
+MP_DECLARE_CONST_FUN_OBJ(mp_op_setitem_obj);
+MP_DECLARE_CONST_FUN_OBJ(mp_op_delitem_obj);
 
 extern const mp_obj_module_t mp_module___main__;
 extern const mp_obj_module_t mp_module_array;
diff --git a/py/mkrules.mk b/py/mkrules.mk
index ab4514d1c4..08ba8fc416 100644
--- a/py/mkrules.mk
+++ b/py/mkrules.mk
@@ -59,7 +59,7 @@ $(BUILD)/%.pp: %.c
 # object directories (but only for existance), and the object directories
 # will be created if they don't exist.
 OBJ_DIRS = $(sort $(dir $(OBJ)))
-$(OBJ): | $(OBJ_DIRS)
+$(OBJ): $(PY_BUILD)/qstrdefs.generated.h | $(OBJ_DIRS)
 $(OBJ_DIRS):
 	$(MKDIR) -p $@
 
diff --git a/py/modsys.c b/py/modsys.c
index 10efd6004d..41ade1f275 100644
--- a/py/modsys.c
+++ b/py/modsys.c
@@ -6,6 +6,7 @@
 #include "runtime.h"
 #include "objlist.h"
 #include "objtuple.h"
+#include "objstr.h"
 
 #if MICROPY_ENABLE_MOD_SYS
 
@@ -20,13 +21,15 @@ mp_obj_list_t mp_sys_path_obj;
 mp_obj_list_t mp_sys_argv_obj;
 #define I(n) MP_OBJ_NEW_SMALL_INT(n)
 // TODO: CPython is now at 5-element array, but save 2 els so far...
-STATIC const mp_obj_tuple_t mp_sys_version_info_obj = {{&mp_type_tuple}, 3, {I(3), I(3), I(5)}};
+STATIC const mp_obj_tuple_t mp_sys_version_info_obj = {{&mp_type_tuple}, 3, {I(3), I(4), I(0)}};
 #undef I
+STATIC const MP_DEFINE_STR_OBJ(version_obj, "3.4.0");
 
 STATIC const mp_map_elem_t mp_module_sys_globals_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR___name__), MP_OBJ_NEW_QSTR(MP_QSTR_sys) },
     { MP_OBJ_NEW_QSTR(MP_QSTR_path), (mp_obj_t)&mp_sys_path_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_argv), (mp_obj_t)&mp_sys_argv_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_version), (mp_obj_t)&version_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_version_info), (mp_obj_t)&mp_sys_version_info_obj },
 #if MP_ENDIANNESS_LITTLE
     { MP_OBJ_NEW_QSTR(MP_QSTR_byteorder), MP_OBJ_NEW_QSTR(MP_QSTR_little) },
diff --git a/py/objdict.c b/py/objdict.c
index 2c56540d15..19d9ae9e9f 100644
--- a/py/objdict.c
+++ b/py/objdict.c
@@ -497,6 +497,8 @@ STATIC const mp_map_elem_t dict_locals_dict_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR_update), (mp_obj_t)&dict_update_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_values), (mp_obj_t)&dict_values_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR___getitem__), (mp_obj_t)&mp_op_getitem_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR___setitem__), (mp_obj_t)&mp_op_setitem_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR___delitem__), (mp_obj_t)&mp_op_delitem_obj },
 };
 
 STATIC MP_DEFINE_CONST_DICT(dict_locals_dict, dict_locals_dict_table);
diff --git a/py/objstr.c b/py/objstr.c
index d933fa5e34..08db2af669 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -10,13 +10,7 @@
 #include "runtime0.h"
 #include "runtime.h"
 #include "pfenv.h"
-
-typedef struct _mp_obj_str_t {
-    mp_obj_base_t base;
-    machine_uint_t hash : 16; // XXX here we assume the hash size is 16 bits (it is at the moment; see qstr.c)
-    machine_uint_t len : 16; // len == number of bytes used in data, alloc = len + 1 because (at the moment) we also append a null byte
-    const byte *data;
-} mp_obj_str_t;
+#include "objstr.h"
 
 STATIC mp_obj_t str_modulo_format(mp_obj_t pattern, uint n_args, const mp_obj_t *args);
 const mp_obj_t mp_const_empty_bytes;
@@ -1463,7 +1457,8 @@ bool mp_obj_str_equal(mp_obj_t s1, mp_obj_t s2) {
     } else {
         GET_STR_HASH(s1, h1);
         GET_STR_HASH(s2, h2);
-        if (h1 != h2) {
+        // If any of hashes is 0, it means it's not valid
+        if (h1 != 0 && h2 != 0 && h1 != h2) {
             return false;
         }
         GET_STR_DATA_LEN(s1, d1, l1);
diff --git a/py/objstr.h b/py/objstr.h
new file mode 100644
index 0000000000..a32ba53b1d
--- /dev/null
+++ b/py/objstr.h
@@ -0,0 +1,10 @@
+typedef struct _mp_obj_str_t {
+    mp_obj_base_t base;
+    // XXX here we assume the hash size is 16 bits (it is at the moment; see qstr.c)
+    machine_uint_t hash : 16;
+    // len == number of bytes used in data, alloc = len + 1 because (at the moment) we also append a null byte
+    machine_uint_t len : 16;
+    const byte *data;
+} mp_obj_str_t;
+
+#define MP_DEFINE_STR_OBJ(obj_name, str) mp_obj_str_t obj_name = {{&mp_type_str}, 0, sizeof(str) - 1, (const byte*)str};
diff --git a/py/opmethods.c b/py/opmethods.c
index af2524cf20..27415fef9b 100644
--- a/py/opmethods.c
+++ b/py/opmethods.c
@@ -13,6 +13,18 @@ STATIC mp_obj_t op_getitem(mp_obj_t lhs_in, mp_obj_t rhs_in) {
 }
 MP_DEFINE_CONST_FUN_OBJ_2(mp_op_getitem_obj, op_getitem);
 
+STATIC mp_obj_t op_setitem(mp_obj_t self_in, mp_obj_t key_in, mp_obj_t value_in) {
+    mp_store_subscr(self_in, key_in, value_in);
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_3(mp_op_setitem_obj, op_setitem);
+
+STATIC mp_obj_t op_delitem(mp_obj_t self_in, mp_obj_t key_in) {
+    mp_store_subscr(self_in, key_in, MP_OBJ_NULL);
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_2(mp_op_delitem_obj, op_delitem);
+
 STATIC mp_obj_t op_contains(mp_obj_t lhs_in, mp_obj_t rhs_in) {
     mp_obj_type_t *type = mp_obj_get_type(lhs_in);
     return type->binary_op(MP_BINARY_OP_IN, lhs_in, rhs_in);
diff --git a/py/qstr.c b/py/qstr.c
index e4b5c111b5..990ff37727 100644
--- a/py/qstr.c
+++ b/py/qstr.c
@@ -35,7 +35,12 @@ machine_uint_t qstr_compute_hash(const byte *data, uint len) {
     for (const byte *top = data + len; data < top; data++) {
         hash = ((hash << 5) + hash) ^ (*data); // hash * 33 ^ data
     }
-    return hash & 0xffff;
+    hash &= 0xffff;
+    // Make sure that valid hash is never zero, zero means "hash not computed"
+    if (hash == 0) {
+        hash++;
+    }
+    return hash;
 }
 
 typedef struct _qstr_pool_t {
diff --git a/py/qstrdefs.h b/py/qstrdefs.h
index df383b776c..80cf681ae7 100644
--- a/py/qstrdefs.h
+++ b/py/qstrdefs.h
@@ -24,6 +24,7 @@ Q(__len__)
 Q(__iter__)
 Q(__getitem__)
 Q(__setitem__)
+Q(__delitem__)
 Q(__add__)
 Q(__sub__)
 Q(__repr__)
@@ -279,6 +280,7 @@ Q(little)
 Q(stdin)
 Q(stdout)
 Q(stderr)
+Q(version)
 Q(version_info)
 #endif