diff --git a/include/pocketpy/pocketpy.h b/include/pocketpy/pocketpy.h
index f40566ff..6ec12130 100644
--- a/include/pocketpy/pocketpy.h
+++ b/include/pocketpy/pocketpy.h
@@ -314,7 +314,6 @@ bool py_callmethod(py_Ref self, py_Name, int argc, py_Ref argv);
 bool py_callmagic(py_Name name, int argc, py_Ref argv);
 
 bool py_str(py_Ref val);
-
 #define py_repr(val) py_callmagic(__repr__, 1, val)
 #define py_len(val) py_callmagic(__len__, 1, val)
 
@@ -327,13 +326,14 @@ py_GlobalRef py_retval();
 /* tuple */
 
 // unchecked functions, if self is not a tuple, the behavior is undefined
+py_ObjectRef py_tuple__data(const py_Ref self);
 py_ObjectRef py_tuple__getitem(const py_Ref self, int i);
 void py_tuple__setitem(py_Ref self, int i, const py_Ref val);
 int py_tuple__len(const py_Ref self);
 
 // unchecked functions, if self is not a list, the behavior is undefined
-py_ObjectRef py_list__getitem(const py_Ref self, int i);
 py_ObjectRef py_list__data(const py_Ref self);
+py_ObjectRef py_list__getitem(const py_Ref self, int i);
 void py_list__setitem(py_Ref self, int i, const py_Ref val);
 void py_list__delitem(py_Ref self, int i);
 int py_list__len(const py_Ref self);
@@ -342,10 +342,6 @@ void py_list__clear(py_Ref self);
 void py_list__insert(py_Ref self, int i, const py_Ref val);
 void py_list__reverse(py_Ref self);
 
-// internal functions
-typedef struct pk_TypeInfo pk_TypeInfo;
-pk_TypeInfo* pk_tpinfo(const py_Ref self);
-
 /// Search the magic method from the given type to the base type.
 /// Return the reference or NULL if not found.
 py_GlobalRef py_tpfindmagic(py_Type, py_Name name);
diff --git a/src/interpreter/ceval.c b/src/interpreter/ceval.c
index 57102e86..6d239d25 100644
--- a/src/interpreter/ceval.c
+++ b/src/interpreter/ceval.c
@@ -497,9 +497,7 @@ pk_FrameResult pk_VM__run_top_frame(pk_VM* self) {
                 c11_sbuf__ctor(&ss);
                 for(int i = 0; i < byte.arg; i++) {
                     if(!py_str(begin + i)) goto __ERROR;
-                    int size;
-                    const char* data = py_tostrn(&self->last_retval, &size);
-                    c11_sbuf__write_cstrn(&ss, data, size);
+                    c11_sbuf__write_sv(&ss, py_tosv(&self->last_retval));
                 }
                 SP() = begin;
                 c11_string* res = c11_sbuf__submit(&ss);
diff --git a/src/interpreter/vm.c b/src/interpreter/vm.c
index 22dd2445..7d058da4 100644
--- a/src/interpreter/vm.c
+++ b/src/interpreter/vm.c
@@ -596,9 +596,7 @@ void pk_print_stack(pk_VM* self, Frame* frame, Bytecode byte) {
                 break;
             }
             case tp_str: {
-                int size;
-                const char* data = py_tostrn(p, &size);
-                pk_sprintf(&buf, "%q", (c11_sv){data, size});
+                pk_sprintf(&buf, "%q", py_tosv(p));
                 break;
             }
             default: {
diff --git a/src/public/py_list.c b/src/public/py_list.c
index 2e3e6cd4..8febf5c2 100644
--- a/src/public/py_list.c
+++ b/src/public/py_list.c
@@ -237,9 +237,7 @@ static bool _py_list__repr__(int argc, py_Ref argv) {
             c11_sbuf__dtor(&buf);
             return false;
         }
-        int size;
-        const char* data = py_tostrn(py_retval(), &size);
-        c11_sbuf__write_cstrn(&buf, data, size);
+        c11_sbuf__write_sv(&buf, py_tosv(py_retval()));
         if(i != self->count - 1) c11_sbuf__write_cstr(&buf, ", ");
     }
     c11_sbuf__write_char(&buf, ']');
diff --git a/src/public/py_str.c b/src/public/py_str.c
index 818243f9..ccf8b504 100644
--- a/src/public/py_str.c
+++ b/src/public/py_str.c
@@ -153,9 +153,7 @@ static bool _py_str__repr__(int argc, py_Ref argv) {
     PY_CHECK_ARGC(1);
     c11_sbuf buf;
     c11_sbuf__ctor(&buf);
-    int size;
-    const char* data = py_tostrn(&argv[0], &size);
-    c11_sbuf__write_quoted(&buf, (c11_sv){data, size}, '\'');
+    c11_sbuf__write_quoted(&buf, py_tosv(&argv[0]), '\'');
     c11_string* res = c11_sbuf__submit(&buf);
     py_newstrn(py_retval(), res->data, res->size);
     c11_string__delete(res);
diff --git a/src/public/py_tuple.c b/src/public/py_tuple.c
index 8aeef3b4..822035c0 100644
--- a/src/public/py_tuple.c
+++ b/src/public/py_tuple.c
@@ -15,6 +15,8 @@ void py_newtuple(py_Ref out, int n) {
 
 py_Ref py_tuple__getitem(const py_Ref self, int i) { return py_getslot(self, i); }
 
+py_Ref py_tuple__data(const py_Ref self) { return PyObject__slots(self->_obj); }
+
 void py_tuple__setitem(py_Ref self, int i, const py_Ref val) { py_setslot(self, i, val); }
 
 int py_tuple__len(const py_Ref self) { return self->_obj->slots; }
@@ -37,9 +39,7 @@ static bool _py_tuple__repr__(int argc, py_Ref argv) {
             c11_sbuf__dtor(&buf);
             return false;
         }
-        int size;
-        const char* data = py_tostrn(py_retval(), &size);
-        c11_sbuf__write_cstrn(&buf, data, size);
+        c11_sbuf__write_sv(&buf, py_tosv(py_retval()));
         if(i != length - 1) c11_sbuf__write_cstr(&buf, ", ");
     }
     if(length == 1) c11_sbuf__write_char(&buf, ',');
diff --git a/src/public/vm.c b/src/public/vm.c
index 8f884583..408ab0d8 100644
--- a/src/public/vm.c
+++ b/src/public/vm.c
@@ -248,11 +248,6 @@ bool py_getunboundmethod(py_Ref self, py_Name name, py_Ref out, py_Ref out_self)
     return false;
 }
 
-pk_TypeInfo* pk_tpinfo(const py_Ref self) {
-    pk_VM* vm = pk_current_vm;
-    return c11__at(pk_TypeInfo, &vm->types, self->type);
-}
-
 py_Ref py_tpfindmagic(py_Type t, py_Name name) {
     assert(py_ismagicname(name));
     pk_TypeInfo* types = (pk_TypeInfo*)pk_current_vm->types.data;