diff --git a/chattool/__init__.py b/chattool/__init__.py
index ab56492..29e94bb 100644
--- a/chattool/__init__.py
+++ b/chattool/__init__.py
@@ -2,7 +2,7 @@
 
 __author__ = """Rex Wang"""
 __email__ = '1073853456@qq.com'
-__version__ = '3.3.1'
+__version__ = '3.3.2'
 
 import os, sys, requests, json
 from .chattype import Chat, Resp
diff --git a/chattool/checkpoint.py b/chattool/checkpoint.py
index d93c34c..274326f 100644
--- a/chattool/checkpoint.py
+++ b/chattool/checkpoint.py
@@ -1,7 +1,8 @@
-import json, warnings, os
+import json, os
 from typing import List, Dict, Union, Callable, Any
 from .chattype import Chat
 import tqdm
+from loguru import logger
 
 def load_chats( checkpoint:str):
     """Load chats from a checkpoint file
@@ -23,18 +24,16 @@ def load_chats( checkpoint:str):
     if len(txts) == 1 and txts[0] == '': return []
     # get the chatlogs
     logs = [json.loads(txt) for txt in txts]
-    chat_size, chatlogs = 1, [None]
-    for log in logs:
-        idx = log['index']
-        if idx >= chat_size: # extend chatlogs
-            chatlogs.extend([None] * (idx - chat_size + 1))
-            chat_size = idx + 1
-        chatlogs[idx] = log['chat_log']
+    # mapping from index to chat object
+    idx2chatlog = { log['index']: Chat(log['chat_log'])  for log in logs }
+    max_index = max(idx2chatlog.keys()) 
+    chat_objects = [ idx2chatlog.get(index, None) for index in range(max_index+1)]
+    num_unfinished = chat_objects.count(None)
     # check if there are missing chatlogs
-    if None in chatlogs:
-        warnings.warn(f"checkpoint file {checkpoint} has unfinished chats")
+    if num_unfinished > 0:
+        logger.warning(f"checkpoint file {checkpoint} has {num_unfinished}/{max_index+1} unfinished chats")
     # return Chat class
-    return [Chat(chat_log) if chat_log is not None else None for chat_log in chatlogs]
+    return chat_objects
 
 def process_chats( data:List[Any]
                  , data2chat:Callable[[Any], Chat]
@@ -59,7 +58,7 @@ def process_chats( data:List[Any]
     ## load chats from the checkpoint file
     chats = load_chats(checkpoint)
     if len(chats) > len(data):
-        warnings.warn(f"checkpoint file {checkpoint} has more chats than the data to be processed")
+        logger.warning(f"checkpoint file {checkpoint} has more chats than the data to be processed")
         return chats[:len(data)]
     chats.extend([None] * (len(data) - len(chats)))
     ## process chats
@@ -69,4 +68,4 @@ def process_chats( data:List[Any]
         chat = data2chat(data[i])
         chat.save(checkpoint, mode='a', index=i)
         chats[i] = chat
-    return chats
\ No newline at end of file
+    return chats
diff --git a/setup.py b/setup.py
index 3ed4b55..5a62168 100644
--- a/setup.py
+++ b/setup.py
@@ -7,7 +7,7 @@
 with open('README.md') as readme_file:
     readme = readme_file.read()
 
-VERSION = '3.3.1'
+VERSION = '3.3.2'
 
 requirements = [
     'Click>=7.0', 'requests>=2.20', "responses>=0.23", 'aiohttp>=3.8',