fix csv logger bug (#21332)

* fix csv logger bug

* address comment

* fix tests

* fix

Author: divyashreepathihalli

keras/src/callbacks/csv_logger.py

@@ -37,6 +37,7 @@ def __init__(self, filename, separator=",", append=False):
         self.writer = None
         self.keys = None
         self.append_header = True
+        self.csv_file = None
 
     def on_train_begin(self, logs=None):
         if self.append:
@@ -46,7 +47,13 @@ def on_train_begin(self, logs=None):
             mode = "a"
         else:
             mode = "w"
+        # ensure csv_file is None or closed before reassigning
+        if self.csv_file and not self.csv_file.closed:
+            self.csv_file.close()
         self.csv_file = file_utils.File(self.filename, mode)
+        # Reset writer and keys
+        self.writer = None
+        self.keys = None
 
     def on_epoch_end(self, epoch, logs=None):
         logs = logs or {}
@@ -65,22 +72,21 @@ def handle_value(k):
 
         if self.keys is None:
             self.keys = sorted(logs.keys())
-            # When validation_freq > 1, `val_` keys are not in first epoch logs
-            # Add the `val_` keys so that its part of the fieldnames of writer.
+
             val_keys_found = False
             for key in self.keys:
                 if key.startswith("val_"):
                     val_keys_found = True
                     break
-            if not val_keys_found:
+            if not val_keys_found and self.keys:
                 self.keys.extend(["val_" + k for k in self.keys])
 
         if not self.writer:
 
             class CustomDialect(csv.excel):
                 delimiter = self.sep
 
-            fieldnames = ["epoch"] + self.keys
+            fieldnames = ["epoch"] + (self.keys or [])
 
             self.writer = csv.DictWriter(
                 self.csv_file, fieldnames=fieldnames, dialect=CustomDialect
@@ -96,5 +102,6 @@ class CustomDialect(csv.excel):
         self.csv_file.flush()
 
     def on_train_end(self, logs=None):
-        self.csv_file.close()
+        if self.csv_file and not self.csv_file.closed:
+            self.csv_file.close()
         self.writer = None