diff --git a/autogen/agentchat/conversable_agent.py b/autogen/agentchat/conversable_agent.py
index fdf42f67b6a3..e086762a419d 100644
--- a/autogen/agentchat/conversable_agent.py
+++ b/autogen/agentchat/conversable_agent.py
@@ -611,25 +611,26 @@ def generate_code_execution_reply(
         if messages is None:
             messages = self._oai_messages[sender]
         last_n_messages = code_execution_config.pop("last_n_messages", 1)
+
+        # iterate through the last n messages reversly
+        # if code blocks are found, execute the code blocks and return the output
+        # if no code blocks are found, continue
         for i in range(min(len(messages), last_n_messages)):
             message = messages[-(i + 1)]
             code_blocks = extract_code(message["content"])
             if len(code_blocks) == 1 and code_blocks[0][0] == UNKNOWN:
-                # no code block is found, lang should be `UNKNOWN`
-
-                if i == last_n_messages - 1:
-                    code_execution_config["last_n_messages"] = last_n_messages
-                    return False, None
                 continue
-                # code_blocks, _ = find_code(messages, sys_msg=self._oai_system_message, **self.llm_config)
-                # if len(code_blocks) == 1 and code_blocks[0][0] == UNKNOWN:
-                #     return code_blocks[0][1]
-            # try to execute the code
+
+            # found code blocks, push last_n_messages back and try to execute the code
+            code_execution_config["last_n_messages"] = last_n_messages
             exitcode, logs = self.execute_code_blocks(code_blocks)
             exitcode2str = "execution succeeded" if exitcode == 0 else "execution failed"
-            break
+            return True, f"exitcode: {exitcode} ({exitcode2str})\nCode output: {logs}"
+
+        # no code blocks are found, push last_n_messages back and return.
         code_execution_config["last_n_messages"] = last_n_messages
-        return True, f"exitcode: {exitcode} ({exitcode2str})\nCode output: {logs}"
+
+        return False, None
 
     def generate_function_call_reply(
         self,
diff --git a/autogen/code_utils.py b/autogen/code_utils.py
index 1a6b970c6427..98a0f44a7966 100644
--- a/autogen/code_utils.py
+++ b/autogen/code_utils.py
@@ -31,7 +31,14 @@ def infer_lang(code):
     """
     if code.startswith("python ") or code.startswith("pip") or code.startswith("python3 "):
         return "sh"
-    return "python"
+
+    # check if code is a valid python code
+    try:
+        compile(code, "test", "exec")
+        return "python"
+    except SyntaxError:
+        # not a valid python code
+        return UNKNOWN
 
 
 def extract_code(
@@ -252,7 +259,7 @@ def execute_code(
     file_dir = os.path.dirname(filepath)
     os.makedirs(file_dir, exist_ok=True)
     if code is not None:
-        with open(filepath, "w") as fout:
+        with open(filepath, "w", encoding="utf-8") as fout:
             fout.write(code)
     # check if already running in a docker container
     in_docker_container = os.path.exists("/.dockerenv")