diff --git a/src/labelme2yolo/l2y.py b/src/labelme2yolo/l2y.py
index a7a03a4..04bd82a 100644
--- a/src/labelme2yolo/l2y.py
+++ b/src/labelme2yolo/l2y.py
@@ -66,10 +66,7 @@ def img_arr_to_b64(img_arr):
     file = io.BytesIO()
     img_pil.save(file, format="PNG")
     img_bin = file.getvalue()
-    if hasattr(base64, "encodebytes"):
-        img_b64 = base64.encodebytes(img_bin)
-    else:
-        img_b64 = base64.encodestring(img_bin)
+    img_b64 = base64.encodebytes(img_bin)
     return img_b64
 
 
@@ -93,7 +90,8 @@ def get_label_id_map(json_dir: str):
     for file_name in os.listdir(json_dir):
         if file_name.endswith("json"):
             json_path = os.path.join(json_dir, file_name)
-            data = json.load(open(json_path))
+            with open(json_path, encoding="utf-8") as file:
+                data = json.load(file)
             for shape in data["shapes"]:
                 label_set.add(shape["label"])
 
@@ -102,13 +100,11 @@ def get_label_id_map(json_dir: str):
 
 def extend_point_list(point_list, out_format="polygon"):
     '''Extend point list to polygon or bbox'''
-    xmin = min([float(point) for point in point_list[::2]])
-    xmax = max([float(point) for point in point_list[::2]])
-    ymin = min([float(point) for point in point_list[1::2]])
-    ymax = max([float(point) for point in point_list[1::2]])
+    xmin = min(float(point) for point in point_list[::2])
+    xmax = max(float(point) for point in point_list[::2])
+    ymin = min(float(point) for point in point_list[1::2])
+    ymax = max(float(point) for point in point_list[1::2])
 
-    if out_format == "polygon":
-        return np.array([xmin, ymin, xmax, ymin, xmax, ymax, xmin, ymax])
     if out_format == "bbox":
         x = xmin
         y = ymin
@@ -118,6 +114,8 @@ def extend_point_list(point_list, out_format="polygon"):
         y = y + h / 2
         return np.array([x, y, w, h])
 
+    return np.array([xmin, ymin, xmax, ymin, xmax, ymax, xmin, ymax])
+
 
 def save_yolo_label(json_name, label_dir_path, target_dir, yolo_obj_list):
     '''Save yolo label to txt file'''
@@ -125,7 +123,7 @@ def save_yolo_label(json_name, label_dir_path, target_dir, yolo_obj_list):
                             target_dir,
                             json_name.replace(".json", ".txt"))
 
-    with open(txt_path, "w+") as f:
+    with open(txt_path, "w+", encoding="utf-8") as f:
         for yolo_obj in yolo_obj_list:
             label, points = yolo_obj
             points = [str(item) for item in points]
@@ -154,19 +152,22 @@ def save_yolo_image(json_data, json_path, image_dir_path, target_dir):
     return img_path
 
 
-class Labelme2YOLO(object):
+class Labelme2YOLO:
     '''Labelme to YOLO format converter'''
+
     def __init__(self, json_dir, output_format, label_list):
         self._json_dir = json_dir
         self._output_format = output_format
         self._label_list = label_list
+        self._label_dir_path = ""
+        self._image_dir_path = ""
 
         if label_list:
             self._label_id_map = {label: label_id
                                   for label_id, label in enumerate(label_list)}
         else:
             self._label_id_map = get_label_id_map(self._json_dir)
-            self._label_list = [label for label in self._label_id_map.keys()]
+            self._label_list = list(self._label_id_map.keys())
 
     def _make_train_val_dir(self):
         self._label_dir_path = os.path.join(self._json_dir,
@@ -186,7 +187,10 @@ def _make_train_val_dir(self):
             os.makedirs(yolo_path)
 
     def _train_test_split(self, folders, json_names, val_size, test_size):
-        if len(folders) > 0 and 'train' in folders and 'val' in folders and 'test' in folders:  # noqa: E501
+        if (len(folders) > 0 and
+            'train' in folders and
+            'val' in folders and
+                'test' in folders):
             train_folder = os.path.join(self._json_dir, 'train/')
             train_json_names = [train_sample_name + '.json'
                                 for train_sample_name in os.listdir(train_folder)
@@ -219,6 +223,7 @@ def _train_test_split(self, folders, json_names, val_size, test_size):
         return train_json_names, val_json_names, test_json_names
 
     def convert(self, val_size, test_size):
+        '''Convert labelme format to yolo format'''
         json_names = [file_name for file_name in os.listdir(self._json_dir)
                       if os.path.isfile(os.path.join(self._json_dir, file_name)) and
                       file_name.endswith('.json')]
@@ -233,23 +238,24 @@ def convert(self, val_size, test_size):
         # also get image from labelme json file and save them under images folder
         for target_dir, json_names in zip(('train/', 'val/', 'test/'),
                                           (train_json_names, val_json_names, test_json_names)):  # noqa: E501
-            pool = Pool(NUM_THREADS)
 
-            for json_name in json_names:
-                pool.apply_async(self.covert_json_to_text,
-                                 args=(target_dir, json_name))
-            pool.close()
-            pool.join()
+            with Pool(NUM_THREADS) as pool:
+                for json_name in json_names:
+                    pool.apply_async(self.covert_json_to_text,
+                                     args=(target_dir, json_name))
+                pool.close()
+                pool.join()
 
         print('Generating dataset.yaml file ...')
         self._save_dataset_yaml()
 
     def covert_json_to_text(self, target_dir, json_name):
+        """Convert json file to yolo format text file and save them to files"""
         json_path = os.path.join(self._json_dir, json_name)
-        json_data = json.load(open(json_path))
+        with open(json_path, encoding="utf-8") as f:
+            json_data = json.load(f)
 
-        print('Converting %s for %s ...' %
-              (json_name, target_dir.replace('/', '')))
+        print(f"Converting {json_name} for {target_dir.replace('/', '')} ...")
 
         img_path = save_yolo_image(json_data,
                                    json_path,