diff --git a/CHANGELOG.md b/CHANGELOG.md
index 89398a06c..03c019944 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ All notable changes to this project will be documented in this file.
 - Matter add controller's Vendor Name to logs and UI
 - Matter redesigned UI
 - Matter add support for Contact Sensor
+- Berry `string.format()` now automatically converts type according to format
 
 ### Breaking Changed
 
diff --git a/lib/libesp32/berry/src/be_baselib.c b/lib/libesp32/berry/src/be_baselib.c
index 592d74a53..ba366c12b 100644
--- a/lib/libesp32/berry/src/be_baselib.c
+++ b/lib/libesp32/berry/src/be_baselib.c
@@ -18,7 +18,7 @@
 
 #define READLINE_STEP       100
 
-static int l_assert(bvm *vm)
+int be_baselib_assert(bvm *vm)
 {
     int argc = be_top(vm);
     /* assertion fails when there is no argument
@@ -33,7 +33,7 @@ static int l_assert(bvm *vm)
     be_return_nil(vm);
 }
 
-static int l_print(bvm *vm)
+int be_baselib_print(bvm *vm)
 {
     int i, argc = be_top(vm);
     for (i = 1; i <= argc; ++i) {
@@ -68,7 +68,7 @@ static int m_readline(bvm *vm)
     be_return(vm);
 }
 
-static int l_input(bvm *vm)
+int be_baselib_input(bvm *vm)
 {
     if (be_top(vm) && be_isstring(vm, 1)) { /* echo prompt */
         be_writestring(be_tostring(vm, 1));
@@ -118,7 +118,7 @@ static bbool obj2int(bvm *vm, bvalue *var, bint *val)
     return bfalse;
 }
 
-static int l_super(bvm *vm)
+int be_baselib_super(bvm *vm)
 {
     int argc = be_top(vm);
 
@@ -197,7 +197,7 @@ static int l_super(bvm *vm)
     be_return_nil(vm);
 }
 
-static int l_type(bvm *vm)
+int be_baselib_type(bvm *vm)
 {
     if (be_top(vm)) {
         be_pushstring(vm, be_typename(vm, 1));
@@ -206,7 +206,7 @@ static int l_type(bvm *vm)
     be_return_nil(vm);
 }
 
-static int l_classname(bvm *vm)
+int be_baselib_classname(bvm *vm)
 {
     if (be_top(vm)) {
         const char *t = be_classname(vm, 1);
@@ -218,7 +218,7 @@ static int l_classname(bvm *vm)
     be_return_nil(vm);
 }
 
-static int l_classof(bvm *vm)
+int be_baselib_classof(bvm *vm)
 {
     if (be_top(vm) && be_classof(vm, 1)) {
         be_return(vm);
@@ -226,7 +226,7 @@ static int l_classof(bvm *vm)
     be_return_nil(vm);
 }
 
-static int l_number(bvm *vm)
+int be_baselib_number(bvm *vm)
 {
     if (be_top(vm)) {
         if (be_isstring(vm, 1)) {
@@ -240,7 +240,7 @@ static int l_number(bvm *vm)
     be_return_nil(vm);
 }
 
-static int l_int(bvm *vm)
+int be_baselib_int(bvm *vm)
 {
     if (be_top(vm)) {
         if (be_isstring(vm, 1)) {
@@ -272,7 +272,7 @@ static int l_int(bvm *vm)
     be_return_nil(vm);
 }
 
-static int l_real(bvm *vm)
+int be_baselib_real(bvm *vm)
 {
     if (be_top(vm)) {
         if (be_isstring(vm, 1)) {
@@ -296,7 +296,7 @@ static int check_method(bvm *vm, const char *attr)
         be_isinstance(vm, 1) && be_getmethod(vm, 1, attr);
 }
 
-static int l_iterator(bvm *vm)
+int be_baselib_iterator(bvm *vm)
 {
     if (be_top(vm) && be_isfunction(vm, 1)) {
         be_return(vm); /* return the argument[0]::function */
@@ -357,7 +357,7 @@ static int l_call(bvm *vm)
     be_return_nil(vm);
 }
 
-static int l_str(bvm *vm)
+int be_baselib_str(bvm *vm)
 {
     if (be_top(vm)) {
         be_tostring(vm, 1);
@@ -378,7 +378,7 @@ static int l_bool(bvm *vm)
 }
 
 
-static int l_size(bvm *vm)
+int be_baselib_size(bvm *vm)
 {
     if (be_top(vm) && be_isstring(vm, 1)) {
         be_pushint(vm, be_strlen(vm, 1));
@@ -393,7 +393,7 @@ static int l_size(bvm *vm)
     be_return_nil(vm);
 }
 
-static int l_module(bvm *vm)
+int be_baselib_module(bvm *vm)
 {
     int argc = be_top(vm);
     be_newmodule(vm);
@@ -436,7 +436,7 @@ static int m_compile_file(bvm *vm)
 }
 #endif
 
-static int l_compile(bvm *vm)
+int be_baselib_compile(bvm *vm)
 {
 #if BE_USE_SCRIPT_COMPILER
     if (be_top(vm) && be_isstring(vm, 1)) {
@@ -467,12 +467,12 @@ static int _issubv(bvm *vm, bbool (*filter)(bvm*, int))
     be_return(vm);
 }
 
-static int l_issubclass(bvm *vm)
+int be_baselib_issubclass(bvm *vm)
 {
     return _issubv(vm, be_isclass);
 }
 
-static int l_isinstance(bvm *vm)
+int be_baselib_isinstance(bvm *vm)
 {
     return _issubv(vm, be_isinstance);
 }
@@ -480,23 +480,23 @@ static int l_isinstance(bvm *vm)
 #if !BE_USE_PRECOMPILED_OBJECT
 void be_load_baselib(bvm *vm)
 {
-    be_regfunc(vm, "assert", l_assert);
-    be_regfunc(vm, "print", l_print);
-    be_regfunc(vm, "input", l_input);
-    be_regfunc(vm, "super", l_super);
-    be_regfunc(vm, "type", l_type);
-    be_regfunc(vm, "classname", l_classname);
-    be_regfunc(vm, "classof", l_classof);
-    be_regfunc(vm, "number", l_number);
-    be_regfunc(vm, "str", l_str);
-    be_regfunc(vm, "int", l_int);
-    be_regfunc(vm, "real", l_real);
-    be_regfunc(vm, "module", l_module);
-    be_regfunc(vm, "size", l_size);
-    be_regfunc(vm, "compile", l_compile);
-    be_regfunc(vm, "issubclass", l_issubclass);
-    be_regfunc(vm, "isinstance", l_isinstance);
-    be_regfunc(vm, "__iterator__", l_iterator);
+    be_regfunc(vm, "assert", be_baselib_assert);
+    be_regfunc(vm, "print", be_baselib_print);
+    be_regfunc(vm, "input", be_baselib_input);
+    be_regfunc(vm, "super", be_baselib_super);
+    be_regfunc(vm, "type", be_baselib_type);
+    be_regfunc(vm, "classname", be_baselib_classname);
+    be_regfunc(vm, "classof", be_baselib_classof);
+    be_regfunc(vm, "number", be_baselib_number);
+    be_regfunc(vm, "str", be_baselib_str);
+    be_regfunc(vm, "int", be_baselib_int);
+    be_regfunc(vm, "real", be_baselib_real);
+    be_regfunc(vm, "module", be_baselib_module);
+    be_regfunc(vm, "size", be_baselib_size);
+    be_regfunc(vm, "compile", be_baselib_compile);
+    be_regfunc(vm, "issubclass", be_baselib_issubclass);
+    be_regfunc(vm, "isinstance", be_baselib_isinstance);
+    be_regfunc(vm, "__iterator__", be_baselib_iterator);
 }
 
 /* call must be added later to respect order of builtins */
@@ -513,23 +513,23 @@ extern const bclass be_class_bytes;
 extern int be_nfunc_open(bvm *vm);
 /* @const_object_info_begin
 vartab m_builtin (scope: local) {
-    assert, func(l_assert)
-    print, func(l_print)
-    input, func(l_input)
-    super, func(l_super)
-    type, func(l_type)
-    classname, func(l_classname)
-    classof, func(l_classof)
-    number, func(l_number)
-    str, func(l_str)
-    int, func(l_int)
-    real, func(l_real)
-    module, func(l_module)
-    size, func(l_size)
-    compile, func(l_compile)
-    issubclass, func(l_issubclass)
-    isinstance, func(l_isinstance)
-    __iterator__, func(l_iterator)
+    assert, func(be_baselib_assert)
+    print, func(be_baselib_print)
+    input, func(be_baselib_input)
+    super, func(be_baselib_super)
+    type, func(be_baselib_type)
+    classname, func(be_baselib_classname)
+    classof, func(be_baselib_classof)
+    number, func(be_baselib_number)
+    str, func(be_baselib_str)
+    int, func(be_baselib_int)
+    real, func(be_baselib_real)
+    module, func(be_baselib_module)
+    size, func(be_baselib_size)
+    compile, func(be_baselib_compile)
+    issubclass, func(be_baselib_issubclass)
+    isinstance, func(be_baselib_isinstance)
+    __iterator__, func(be_baselib_iterator)
     open, func(be_nfunc_open)
     list, class(be_class_list)
     map, class(be_class_map)
diff --git a/lib/libesp32/berry/src/be_baselib.h b/lib/libesp32/berry/src/be_baselib.h
new file mode 100644
index 000000000..582b0871b
--- /dev/null
+++ b/lib/libesp32/berry/src/be_baselib.h
@@ -0,0 +1,31 @@
+/********************************************************************
+** Copyright (c) 2018-2020 Guan Wenliang
+** This file is part of the Berry default interpreter.
+** skiars@qq.com, https://github.com/Skiars/berry
+** See Copyright Notice in the LICENSE file or at
+** https://github.com/Skiars/berry/blob/master/LICENSE
+********************************************************************/
+#ifndef __BE_BASELIB_H
+#define __BE_BASELIB_H
+
+#include "be_object.h"
+
+int be_baselib_assert(bvm *vm);
+int be_baselib_print(bvm *vm);
+int be_baselib_input(bvm *vm);
+int be_baselib_super(bvm *vm);
+int be_baselib_type(bvm *vm);
+int be_baselib_classname(bvm *vm);
+int be_baselib_classof(bvm *vm);
+int be_baselib_number(bvm *vm);
+int be_baselib_str(bvm *vm);
+int be_baselib_int(bvm *vm);
+int be_baselib_real(bvm *vm);
+int be_baselib_module(bvm *vm);
+int be_baselib_size(bvm *vm);
+int be_baselib_compile(bvm *vm);
+int be_baselib_issubclass(bvm *vm);
+int be_baselib_isinstance(bvm *vm);
+int be_baselib_iterator(bvm *vm);
+
+#endif
diff --git a/lib/libesp32/berry/src/be_strlib.c b/lib/libesp32/berry/src/be_strlib.c
index 2c5424634..4172876e6 100644
--- a/lib/libesp32/berry/src/be_strlib.c
+++ b/lib/libesp32/berry/src/be_strlib.c
@@ -12,6 +12,7 @@
 #include "be_module.h"
 #include "be_exec.h"
 #include "be_mem.h"
+#include "be_baselib.h"
 #include <string.h>
 #include <stdio.h>
 #include <ctype.h>
@@ -556,6 +557,48 @@ static void mode_fixlen(char *mode, const char *lenmode)
     mode[l + lm] = '\0';
 }
 
+static bbool convert_to_int(bvm *vm, int index, bint *val)
+{
+    bbool converted = bfalse;
+    if (val == NULL) { return bfalse; }
+    if (be_isint(vm, index)) {
+        *val = be_toint(vm, index);
+        converted = btrue;
+    } else {
+        be_pushntvfunction(vm, be_baselib_int);
+        be_pushvalue(vm, index);
+        be_call(vm, 1);
+        be_pop(vm, 1);
+        if (be_isint(vm, -1)) {
+            *val = be_toint(vm, -1);
+            converted = btrue;
+        }
+        be_pop(vm, 1);
+    }
+    return converted;
+}
+
+static bbool convert_to_real(bvm *vm, int index, breal *val)
+{
+    bbool converted = bfalse;
+    if (val == NULL) { return bfalse; }
+    if (be_isnumber(vm, index)) {
+        *val = be_toreal(vm, index);
+        converted = btrue;
+    } else {
+        be_pushntvfunction(vm, be_baselib_real);
+        be_pushvalue(vm, index);
+        be_call(vm, 1);
+        be_pop(vm, 1);
+        if (be_isnumber(vm, -1)) {
+            *val = be_toreal(vm, -1);
+            converted = btrue;
+        }
+        be_pop(vm, 1);
+    }
+    return converted;
+}
+
 static int str_format(bvm *vm)
 {
     int top = be_top(vm);
@@ -585,25 +628,34 @@ static int str_format(bvm *vm)
                 break;
             case 'd': case 'i': case 'o':
             case 'u': case 'x': case 'X':
-                if (be_isint(vm, index)) {
+            {
+                bint val;
+                if (convert_to_int(vm, index, &val)) {
                     mode_fixlen(mode, BE_INT_FMTLEN);
-                    sprintf(buf, mode, be_toint(vm, index));
+                    sprintf(buf, mode, val);
                 }
                 be_pushstring(vm, buf);
                 break;
+            }
             case 'e': case 'E':
             case 'f': case 'g': case 'G':
-                if (be_isnumber(vm, index)) {
-                    sprintf(buf, mode, be_toreal(vm, index));
+            {
+                breal val;
+                if (convert_to_real(vm, index, &val)) {
+                    sprintf(buf, mode, val);
                 }
                 be_pushstring(vm, buf);
                 break;
+            }
             case 'c':
-                if (be_isint(vm, index)) {
-                    sprintf(buf, "%c", (int)be_toint(vm, index));
+            {
+                bint val;
+                if (convert_to_int(vm, index, &val)) {
+                    sprintf(buf, "%c", (int)val);
                 }
                 be_pushstring(vm, buf);
                 break;
+            }
             case 's': {
                 const char *s = be_tostring(vm, index);
                 int len = be_strlen(vm, index);
diff --git a/lib/libesp32/berry/tests/string.be b/lib/libesp32/berry/tests/string.be
index e7d91e8dd..072e5faa7 100644
--- a/lib/libesp32/berry/tests/string.be
+++ b/lib/libesp32/berry/tests/string.be
@@ -110,3 +110,40 @@ s = "a"#
     "b"  # zz
     "c"
 assert(s == 'abc')
+
+# string.format with automatic conversion
+import string
+
+assert(string.format("%i", 3) == '3')
+assert(string.format("%i", "3") == '3')
+assert(string.format("%i", "03") == '3')
+assert(string.format("%i", nil) == '')
+
+class A def toint() return 42 end end
+a=A()
+class B end
+b=B()
+
+assert(string.format("%i", a) == '42')
+assert(string.format("%i", b) == '')
+
+assert(string.format("%i", nil) == '')
+assert(string.format("%i", true) == '1')
+assert(string.format("%i", false) == '0')
+
+assert(string.format("%c", a) == '*')
+
+assert(string.format("%f", 3.5) == '3.500000')
+assert(string.format("%f", 3) == '3.000000')
+assert(string.format("%.1f", 3) == '3.0')
+assert(string.format("%.1f", nil) == '')
+assert(string.format("%.1f", true) == '')
+assert(string.format("%.1f", false) == '')
+assert(string.format("%.1f", a) == '')
+
+assert(string.format("%s", a) == '<instance: A()>')
+assert(string.format("%s", 0) == '0')
+assert(string.format("%s", nil) == 'nil')
+assert(string.format("%s", true) == 'true')
+assert(string.format("%s", false) == 'false')
+