diff --git a/verl/utils/dataset.py b/verl/utils/dataset.py
index 95046c29..91a9b419 100644
--- a/verl/utils/dataset.py
+++ b/verl/utils/dataset.py
@@ -20,8 +20,8 @@
 
 import numpy as np
 import torch
-from jinja2 import Template
 from datasets import load_dataset
+from jinja2 import Template
 from PIL import Image
 from PIL.Image import Image as ImageObject
 from torch.utils.data import Dataset
@@ -127,7 +127,7 @@ def __init__(
                 self.format_prompt = f.read()
 
         if self.filter_overlong_prompts:
-            self.dataset = self.dataset.filter(self._filter_overlong_prompts, desc=f"Filtering overlong prompts")
+            self.dataset = self.dataset.filter(self._filter_overlong_prompts, desc="Filtering overlong prompts")
 
     def _get_messages(self, example: Dict[str, Any]) -> List[Dict[str, Any]]:
         prompt_str: str = example[self.prompt_key]
@@ -152,7 +152,9 @@ def _get_messages(self, example: Dict[str, Any]) -> List[Dict[str, Any]]:
     def _filter_overlong_prompts(self, example: Dict[str, Any]) -> bool:
         messages = self._get_messages(example)
         processing_class = self.processor if self.processor is not None else self.tokenizer
-        return len(processing_class.apply_chat_template(messages, add_generation_prompt=True)) <= self.max_prompt_length
+        return (
+            len(processing_class.apply_chat_template(messages, add_generation_prompt=True)) <= self.max_prompt_length
+        )
 
     def __len__(self):
         return len(self.dataset)
@@ -198,9 +200,9 @@ def __getitem__(self, index):
         raw_prompt_ids = self.tokenizer.encode(prompt, add_special_tokens=False)
         if len(raw_prompt_ids) > self.max_prompt_length:
             if self.truncation == "left":
-                raw_prompt_ids = raw_prompt_ids[..., -self.max_prompt_length:]
+                raw_prompt_ids = raw_prompt_ids[..., -self.max_prompt_length :]
             elif self.truncation == "right":
-                raw_prompt_ids = raw_prompt_ids[..., :self.max_prompt_length]
+                raw_prompt_ids = raw_prompt_ids[..., : self.max_prompt_length]
             elif self.truncation == "error":
                 raise RuntimeError(f"Prompt length {len(raw_prompt_ids)} is longer than {self.max_prompt_length}.")