diff --git a/package/PikaStdLib/PikaStdData.pyi b/package/PikaStdLib/PikaStdData.pyi
index 208af718f..5b1e6def1 100644
--- a/package/PikaStdLib/PikaStdData.pyi
+++ b/package/PikaStdLib/PikaStdData.pyi
@@ -2,104 +2,60 @@ from PikaObj import *
 
 
 class List(TinyObj):
-    def __init__(self):
-        pass
-
+    def __init__(self): ...
     # add an arg after the end of list
-    def append(self, arg: any):
-        pass
-
+    def append(self, arg: any): ...
     # get an arg by the index
-    def get(self, i: int) -> any:
-        pass
-
+    def get(self, i: int) -> any: ...
     # set an arg by the index
-    def set(self, i: int, arg: any):
-        pass
-
+    def set(self, i: int, arg: any): ...
     # get the length of list
-    def len(self) -> int:
-        pass
-
+    def len(self) -> int: ...
     # support for loop
-    def __iter__(self) -> any:
-        pass
-
+    def __iter__(self) -> any: ...
     # support for loop
-    def __next__(self) -> any:
-        pass
-
+    def __next__(self) -> any: ...
     # support list[]  = val
-    def __set__(self, __key: any, __val: any):
-        pass
-
+    def __set__(self, __key: any, __val: any): ...
     # support val = list[]
-    def __get__(self, __key: any) -> any:
-        pass
+    def __get__(self, __key: any) -> any: ...
 
 
 class Dict(TinyObj):
-    def __init__(self):
-        pass
-
+    def __init__(self): ...
     # get an arg by the key
-    def get(self, key: str) -> any:
-        pass
-
+    def get(self, key: str) -> any: ...
     # set an arg by the key
-    def set(self, key: str, arg: any):
-        pass
-
+    def set(self, key: str, arg: any): ...
     # remove an arg by the key
-    def remove(self, key: str):
-        pass
-
-    def __iter__(self) -> any:
-        pass
-
-    def __next__(self) -> any:
-        pass
-
+    def remove(self, key: str): ...
+    def __iter__(self) -> any: ...
+    def __next__(self) -> any: ...
     # support dict[]  = val
-    def __set__(self, __key: any, __val: any):
-        pass
-
+    def __set__(self, __key: any, __val: any): ...
     # support val = dict[]
-    def __get__(self, __key: any) -> any:
-        pass
+    def __get__(self, __key: any) -> any: ...
 
 
 class String(TinyObj):
-    def __init__(self, s: str):
-        pass
-
-    def set(self, s: str):
-        pass
-
-    def get(self) -> str:
-        pass
-
-    def __iter__(self) -> any:
-        pass
-
-    def __next__(self) -> any:
-        pass
-
+    def __init__(self, s: str): ...
+    def set(self, s: str): ...
+    def get(self) -> str: ...
+    def __iter__(self) -> any: ...
+    def __next__(self) -> any: ...
     # support string[]  = val
-    def __set__(self, __key: any, __val: any):
-        pass
-
+    def __set__(self, __key: any, __val: any): ...
     # support val = string[]
-    def __get__(self, __key: any) -> any:
-        pass
+    def __get__(self, __key: any) -> any: ...
+    # support str()
+    def __str__(self) -> str: ...
 
 
 class ByteArray(List):
     # convert a string to ByteArray
-    def fromString(self, s: str):
-        pass
+    def fromString(self, s: str): ...
 
 
 class Utils(TinyObj):
-    def int_to_bytes(self, val: int) -> bytes:
-        pass
+    # convert a int to bytes
+    def int_to_bytes(self, val: int) -> bytes: ...
diff --git a/package/PikaStdLib/PikaStdData_String.c b/package/PikaStdLib/PikaStdData_String.c
index d796e3ebe..8b1f8756c 100644
--- a/package/PikaStdLib/PikaStdData_String.c
+++ b/package/PikaStdLib/PikaStdData_String.c
@@ -1,4 +1,4 @@
-#include "PikaObj.h"
+#include "PikaStdData_String.h"
 
 Arg* PikaStdData_String___iter__(PikaObj* self) {
     obj_setInt(self, "__iter_i", 0);
@@ -33,8 +33,8 @@ Arg* PikaStdData_String___next__(PikaObj* self) {
     return res;
 }
 
-Arg* PikaStdData_String___get__(PikaObj* self) {
-    int key_i = obj_getInt(self, "__key");
+Arg* PikaStdData_String___get__(PikaObj* self, Arg* __key) {
+    int key_i = arg_getInt(__key);
     char* str = obj_getStr(self, "str");
     uint16_t len = strGetSize(str);
     char char_buff[] = " ";
@@ -46,4 +46,19 @@ Arg* PikaStdData_String___get__(PikaObj* self) {
     }
 }
 
-void PikaStdData_String___set__(PikaObj* self) {}
+void PikaStdData_String___set__(PikaObj* self, Arg* __key, Arg* __val) {
+    int key_i = arg_getInt(__key);
+    char* str = obj_getStr(self, "str");
+    char* val = arg_getStr(__val);
+    uint16_t len = strGetSize(str);
+    if (key_i >= len) {
+        obj_setErrorCode(self, 1);
+        __platform_printf("Error String Overflow\r\n");
+        return;
+    }
+    str[key_i] = val[0];
+}
+
+char* PikaStdData_String___str__(PikaObj* self) {
+    return obj_getStr(self, "str");
+}
diff --git a/package/PikaStdLib/PikaStdLib_SysObj.c b/package/PikaStdLib/PikaStdLib_SysObj.c
index 967393884..a364dbf34 100644
--- a/package/PikaStdLib/PikaStdLib_SysObj.c
+++ b/package/PikaStdLib/PikaStdLib_SysObj.c
@@ -116,7 +116,7 @@ char* PikaStdLib_SysObj_str(PikaObj* self, Arg* arg) {
         res = strsFormat(&buffs, 11, "%f", val);
         goto exit;
     }
-    if (ARG_TYPE_OBJECT == type) {
+    if (argType_isObject(type)) {
         res = obj_toStr(arg_getPtr(arg));
         if (NULL != res) {
             goto exit;
diff --git a/port/linux/package/pikascript/PikaStdData.pyi b/port/linux/package/pikascript/PikaStdData.pyi
index 208af718f..5b1e6def1 100644
--- a/port/linux/package/pikascript/PikaStdData.pyi
+++ b/port/linux/package/pikascript/PikaStdData.pyi
@@ -2,104 +2,60 @@ from PikaObj import *
 
 
 class List(TinyObj):
-    def __init__(self):
-        pass
-
+    def __init__(self): ...
     # add an arg after the end of list
-    def append(self, arg: any):
-        pass
-
+    def append(self, arg: any): ...
     # get an arg by the index
-    def get(self, i: int) -> any:
-        pass
-
+    def get(self, i: int) -> any: ...
     # set an arg by the index
-    def set(self, i: int, arg: any):
-        pass
-
+    def set(self, i: int, arg: any): ...
     # get the length of list
-    def len(self) -> int:
-        pass
-
+    def len(self) -> int: ...
     # support for loop
-    def __iter__(self) -> any:
-        pass
-
+    def __iter__(self) -> any: ...
     # support for loop
-    def __next__(self) -> any:
-        pass
-
+    def __next__(self) -> any: ...
     # support list[]  = val
-    def __set__(self, __key: any, __val: any):
-        pass
-
+    def __set__(self, __key: any, __val: any): ...
     # support val = list[]
-    def __get__(self, __key: any) -> any:
-        pass
+    def __get__(self, __key: any) -> any: ...
 
 
 class Dict(TinyObj):
-    def __init__(self):
-        pass
-
+    def __init__(self): ...
     # get an arg by the key
-    def get(self, key: str) -> any:
-        pass
-
+    def get(self, key: str) -> any: ...
     # set an arg by the key
-    def set(self, key: str, arg: any):
-        pass
-
+    def set(self, key: str, arg: any): ...
     # remove an arg by the key
-    def remove(self, key: str):
-        pass
-
-    def __iter__(self) -> any:
-        pass
-
-    def __next__(self) -> any:
-        pass
-
+    def remove(self, key: str): ...
+    def __iter__(self) -> any: ...
+    def __next__(self) -> any: ...
     # support dict[]  = val
-    def __set__(self, __key: any, __val: any):
-        pass
-
+    def __set__(self, __key: any, __val: any): ...
     # support val = dict[]
-    def __get__(self, __key: any) -> any:
-        pass
+    def __get__(self, __key: any) -> any: ...
 
 
 class String(TinyObj):
-    def __init__(self, s: str):
-        pass
-
-    def set(self, s: str):
-        pass
-
-    def get(self) -> str:
-        pass
-
-    def __iter__(self) -> any:
-        pass
-
-    def __next__(self) -> any:
-        pass
-
+    def __init__(self, s: str): ...
+    def set(self, s: str): ...
+    def get(self) -> str: ...
+    def __iter__(self) -> any: ...
+    def __next__(self) -> any: ...
     # support string[]  = val
-    def __set__(self, __key: any, __val: any):
-        pass
-
+    def __set__(self, __key: any, __val: any): ...
     # support val = string[]
-    def __get__(self, __key: any) -> any:
-        pass
+    def __get__(self, __key: any) -> any: ...
+    # support str()
+    def __str__(self) -> str: ...
 
 
 class ByteArray(List):
     # convert a string to ByteArray
-    def fromString(self, s: str):
-        pass
+    def fromString(self, s: str): ...
 
 
 class Utils(TinyObj):
-    def int_to_bytes(self, val: int) -> bytes:
-        pass
+    # convert a int to bytes
+    def int_to_bytes(self, val: int) -> bytes: ...
diff --git a/port/linux/package/pikascript/main.py b/port/linux/package/pikascript/main.py
index 0127628f8..2e7c2ca48 100644
--- a/port/linux/package/pikascript/main.py
+++ b/port/linux/package/pikascript/main.py
@@ -9,7 +9,11 @@ import test_module1
 import test_cmodule
 import TempDevTest as dev
 import TemplateDevice
+from PikaStdData import String
 
+mem = PikaStdLib.MemChecker()
 print('hello pikascript!')
+print('mem used max:')
+mem.max()
 
 dev.test()
diff --git a/port/linux/package/pikascript/pikascript-lib/PikaStdLib/PikaStdData_String.c b/port/linux/package/pikascript/pikascript-lib/PikaStdLib/PikaStdData_String.c
index d796e3ebe..8b1f8756c 100644
--- a/port/linux/package/pikascript/pikascript-lib/PikaStdLib/PikaStdData_String.c
+++ b/port/linux/package/pikascript/pikascript-lib/PikaStdLib/PikaStdData_String.c
@@ -1,4 +1,4 @@
-#include "PikaObj.h"
+#include "PikaStdData_String.h"
 
 Arg* PikaStdData_String___iter__(PikaObj* self) {
     obj_setInt(self, "__iter_i", 0);
@@ -33,8 +33,8 @@ Arg* PikaStdData_String___next__(PikaObj* self) {
     return res;
 }
 
-Arg* PikaStdData_String___get__(PikaObj* self) {
-    int key_i = obj_getInt(self, "__key");
+Arg* PikaStdData_String___get__(PikaObj* self, Arg* __key) {
+    int key_i = arg_getInt(__key);
     char* str = obj_getStr(self, "str");
     uint16_t len = strGetSize(str);
     char char_buff[] = " ";
@@ -46,4 +46,19 @@ Arg* PikaStdData_String___get__(PikaObj* self) {
     }
 }
 
-void PikaStdData_String___set__(PikaObj* self) {}
+void PikaStdData_String___set__(PikaObj* self, Arg* __key, Arg* __val) {
+    int key_i = arg_getInt(__key);
+    char* str = obj_getStr(self, "str");
+    char* val = arg_getStr(__val);
+    uint16_t len = strGetSize(str);
+    if (key_i >= len) {
+        obj_setErrorCode(self, 1);
+        __platform_printf("Error String Overflow\r\n");
+        return;
+    }
+    str[key_i] = val[0];
+}
+
+char* PikaStdData_String___str__(PikaObj* self) {
+    return obj_getStr(self, "str");
+}
diff --git a/port/linux/package/pikascript/pikascript-lib/PikaStdLib/PikaStdLib_SysObj.c b/port/linux/package/pikascript/pikascript-lib/PikaStdLib/PikaStdLib_SysObj.c
index 967393884..a364dbf34 100644
--- a/port/linux/package/pikascript/pikascript-lib/PikaStdLib/PikaStdLib_SysObj.c
+++ b/port/linux/package/pikascript/pikascript-lib/PikaStdLib/PikaStdLib_SysObj.c
@@ -116,7 +116,7 @@ char* PikaStdLib_SysObj_str(PikaObj* self, Arg* arg) {
         res = strsFormat(&buffs, 11, "%f", val);
         goto exit;
     }
-    if (ARG_TYPE_OBJECT == type) {
+    if (argType_isObject(type)) {
         res = obj_toStr(arg_getPtr(arg));
         if (NULL != res) {
             goto exit;
diff --git a/port/linux/test/pikaMain-test.cpp b/port/linux/test/pikaMain-test.cpp
index a44667ae6..ec4265b5d 100644
--- a/port/linux/test/pikaMain-test.cpp
+++ b/port/linux/test/pikaMain-test.cpp
@@ -2090,4 +2090,45 @@ TEST(pikaMain, slice_a12) {
     obj_deinit(self);
     EXPECT_EQ(pikaMemNow(), 0);
 }
-#endif
\ No newline at end of file
+#endif
+
+TEST(pikaMain, str_string) {
+    /* init */
+    pikaMemInfo.heapUsedMax = 0;
+    /* run */
+    PikaObj* self = newRootObj("pikaMain", New_PikaMain);
+    __platform_printf("BEGIN\r\n");
+    obj_run(self, 
+    "a = PikaStdData.String('test')\n"
+    "print(a)\n"
+    );
+    /* assert */
+    EXPECT_STREQ(log_buff[0], "test\r\n");
+    EXPECT_STREQ(log_buff[1], "BEGIN\r\n");
+    /* deinit */
+    obj_deinit(self);
+    EXPECT_EQ(pikaMemNow(), 0);
+}
+
+#if PIKA_SYNTEX_ITEM_SLICE_ENABLE
+TEST(pikaMain, string_index) {
+    /* init */
+    pikaMemInfo.heapUsedMax = 0;
+    /* run */
+    PikaObj* self = newRootObj("pikaMain", New_PikaMain);
+    __platform_printf("BEGIN\r\n");
+    obj_run(self, 
+    "a = PikaStdData.String('test')\n"
+    "a[1]\n"
+    "a[1] = 'q'\n"
+    "print(a)\n"
+    );
+    /* assert */
+    EXPECT_STREQ(log_buff[0], "tqst\r\n");
+    EXPECT_STREQ(log_buff[1], "e\r\n");
+    EXPECT_STREQ(log_buff[2], "BEGIN\r\n");
+    /* deinit */
+    obj_deinit(self);
+    EXPECT_EQ(pikaMemNow(), 0);
+}
+#endif
diff --git a/src/BaseObj.c b/src/BaseObj.c
index 3410f0f81..e72a2507c 100644
--- a/src/BaseObj.c
+++ b/src/BaseObj.c
@@ -59,7 +59,7 @@ void Baseobj_print(PikaObj* self, Args* args) {
             return;
         }
     }
-    if (ARG_TYPE_OBJECT == arg_type) {
+    if (argType_isObject(arg_type)) {
         char* to_str = obj_toStr(arg_getPtr(arg));
         if (NULL != to_str) {
             __platform_printf("%s\r\n", to_str);
diff --git a/src/PikaCompiler.c b/src/PikaCompiler.c
index 98bd3b8cb..3813d9d95 100644
--- a/src/PikaCompiler.c
+++ b/src/PikaCompiler.c
@@ -178,7 +178,7 @@ int LibObj_staticLinkFile(LibObj* self, char* input_file_name) {
 }
 
 static int32_t __foreach_handler_listModules(Arg* argEach, Args* context) {
-    if (arg_getType(argEach) == ARG_TYPE_OBJECT) {
+    if (argType_isObject(arg_getType(argEach))) {
         PikaObj* module_obj = arg_getPtr(argEach);
         __platform_printf("%s\r\n", obj_getStr(module_obj, "name"));
     }
@@ -191,7 +191,7 @@ void LibObj_listModules(LibObj* self) {
 
 static int32_t __foreach_handler_writeBytecode(Arg* argEach, Args* context) {
     FILE* out_file = args_getPtr(context, "out_file");
-    if (arg_getType(argEach) == ARG_TYPE_OBJECT) {
+    if (argType_isObject(arg_getType(argEach))) {
         PikaObj* module_obj = arg_getPtr(argEach);
         char* bytecode = obj_getPtr(module_obj, "bytecode");
         size_t bytecode_size = obj_getBytesSize(module_obj, "buff");
@@ -206,7 +206,7 @@ static int32_t __foreach_handler_writeBytecode(Arg* argEach, Args* context) {
 
 static int32_t __foreach_handler_writeIndex(Arg* argEach, Args* context) {
     FILE* out_file = args_getPtr(context, "out_file");
-    if (arg_getType(argEach) == ARG_TYPE_OBJECT) {
+    if (argType_isObject(arg_getType(argEach))) {
         PikaObj* module_obj = arg_getPtr(argEach);
         uint32_t bytecode_size = obj_getBytesSize(module_obj, "buff");
         char buff[LIB_INFO_BLOCK_SIZE - sizeof(uint32_t)] = {0};
@@ -221,7 +221,7 @@ static int32_t __foreach_handler_writeIndex(Arg* argEach, Args* context) {
 }
 
 static int32_t __foreach_handler_getModuleNum(Arg* argEach, Args* context) {
-    if (arg_getType(argEach) == ARG_TYPE_OBJECT) {
+    if (argType_isObject(arg_getType(argEach))) {
         args_setInt(context, "module_num",
                     args_getInt(context, "module_num") + 1);
     }
@@ -347,8 +347,7 @@ int Lib_loadLibraryFileToArray(char* origin_file_name, char* out_folder) {
     char* array_name = strsGetLastToken(&buffs, origin_file_name, '/');
     array_name = strsReplace(&buffs, array_name, ".", "_");
     __platform_printf("    loading %s[]...\n", array_name);
-    pika_fputs("#include \"PikaPlatform.h\"\n",
-               fp);
+    pika_fputs("#include \"PikaPlatform.h\"\n", fp);
     pika_fputs("/* warning: auto generated file, please do not modify */\n",
                fp);
     pika_fputs("PIKA_BYTECODE_ALIGN const unsigned char ", fp);
@@ -485,7 +484,7 @@ exit:
 }
 
 int32_t __foreach_handler_printStates(Arg* argEach, Args* context) {
-    if (arg_getType(argEach) == ARG_TYPE_OBJECT) {
+    if (argType_isObject(arg_getType(argEach))) {
         PikaObj* module_obj = arg_getPtr(argEach);
         __platform_printf("%s: %s\r\n", obj_getStr(module_obj, "name"),
                           obj_getStr(module_obj, "state"));
@@ -498,7 +497,7 @@ void pikaMaker_printStates(PikaMaker* self) {
 }
 
 int32_t __foreach_handler_getFirstNocompiled(Arg* argEach, Args* context) {
-    if (arg_getType(argEach) == ARG_TYPE_OBJECT) {
+    if (argType_isObject(arg_getType(argEach))) {
         PikaObj* module_obj = arg_getPtr(argEach);
         char* state = obj_getStr(module_obj, "state");
         if (args_isArgExist(context, "res")) {
@@ -544,7 +543,7 @@ void pikaMaker_compileModuleWithDepends(PikaMaker* self, char* module_name) {
 
 int32_t __foreach_handler_linkCompiledModules(Arg* argEach, Args* context) {
     Args buffs = {0};
-    if (arg_getType(argEach) == ARG_TYPE_OBJECT) {
+    if (argType_isObject(arg_getType(argEach))) {
         LibObj* lib = args_getPtr(context, "__lib");
         PikaMaker* maker = args_getPtr(context, "__maker");
         PikaObj* module_obj = arg_getPtr(argEach);
diff --git a/src/PikaObj.c b/src/PikaObj.c
index c564d4922..8104d8cf7 100644
--- a/src/PikaObj.c
+++ b/src/PikaObj.c
@@ -429,7 +429,7 @@ static PikaObj* __obj_getObjDirect(PikaObj* self, char* name) {
         return __obj_initSubObj(self, name);
     }
     /* found Objcet */
-    if (type == ARG_TYPE_OBJECT || type == ARG_TYPE_OBJECT_NEW) {
+    if (argType_isObject(type)) {
         return args_getPtr(self->list, name);
     }
     return NULL;
diff --git a/src/dataArg.c b/src/dataArg.c
index c11aff2fc..9927836a5 100644
--- a/src/dataArg.c
+++ b/src/dataArg.c
@@ -385,3 +385,10 @@ uint8_t* arg_getContent(Arg* self) {
 void arg_setNext(Arg* self, Arg* next) {
     self->next = next;
 }
+
+uint8_t argType_isObject(ArgType type) {
+    if (ARG_TYPE_OBJECT == type || ARG_TYPE_OBJECT_NEW == type) {
+        return 1;
+    }
+    return 0;
+}
diff --git a/src/dataArg.h b/src/dataArg.h
index 0a5796bd9..0cbb2da95 100644
--- a/src/dataArg.h
+++ b/src/dataArg.h
@@ -116,5 +116,6 @@ void arg_deinitHeap(Arg* self);
 Arg* arg_setBytes(Arg* self, char* name, uint8_t* src, size_t size);
 void arg_printBytes(Arg* self);
 Arg* arg_loadFile(Arg* self, char* filename);
+uint8_t argType_isObject(ArgType type);
 
 #endif
diff --git a/src/dataArgs.c b/src/dataArgs.c
index a51e006d4..4adc12d24 100644
--- a/src/dataArgs.c
+++ b/src/dataArgs.c
@@ -434,7 +434,7 @@ char* args_print(Args* self, char* name) {
         goto exit;
     }
 
-    if (type == ARG_TYPE_OBJECT) {
+    if (argType_isObject(type)) {
         void* val = args_getPtr(self, name);
         res = getPrintStringFromPtr(self, name, val);
         goto exit;