diff --git a/vnpy/app/csv_loader/engine.py b/vnpy/app/csv_loader/engine.py
index c0547036..fa88afe7 100644
--- a/vnpy/app/csv_loader/engine.py
+++ b/vnpy/app/csv_loader/engine.py
@@ -41,17 +41,17 @@ class CsvLoaderEngine(BaseEngine):
         """"""
         super().__init__(main_engine, event_engine, APP_NAME)
 
-        self.file_path: str = ''
+        self.file_path: str = ""
 
         self.symbol: str = ""
         self.exchange: Exchange = Exchange.SSE
         self.interval: Interval = Interval.MINUTE
-        self.datetime_head: str = ''
-        self.open_head: str = ''
-        self.close_head: str = ''
-        self.low_head: str = ''
-        self.high_head: str = ''
-        self.volume_head: str = ''
+        self.datetime_head: str = ""
+        self.open_head: str = ""
+        self.close_head: str = ""
+        self.low_head: str = ""
+        self.high_head: str = ""
+        self.volume_head: str = ""
 
     def load(
         self,
@@ -74,7 +74,7 @@ class CsvLoaderEngine(BaseEngine):
         end = None
         count = 0
 
-        with open(file_path, 'rt') as f:
+        with open(file_path, "rt") as f:
             reader = csv.DictReader(f)
 
             db_bars = []