diff --git a/data/data_loader.py b/data/data_loader.py
index 2ee0921..a42f28a 100644
--- a/data/data_loader.py
+++ b/data/data_loader.py
@@ -15,14 +15,11 @@ limitations under the License.
 """
 import bisect
 import logging
-import os.path
-from collections import defaultdict
 import math
 import copy
 
 import random
-from itertools import groupby
-from typing import Tuple, List, Dict
+from typing import List, Dict
 
 from data.image_train_item import ImageTrainItem, DEFAULT_BATCH_ID
 import PIL.Image
@@ -31,37 +28,6 @@ from utils.first_fit_decreasing import first_fit_decreasing
 
 PIL.Image.MAX_IMAGE_PIXELS = 715827880*4 # increase decompression bomb error limit to 4x default
 
-def __chunk(l: List, chunk_size) -> List:
-    num_chunks = int(math.ceil(float(len(l)) / chunk_size))
-    return [l[i * chunk_size:(i + 1) * chunk_size] for i in range(num_chunks)]
-
-def __unchunk(chunked_list: List):
-    return [i for c in chunked_list for i in c]
-
-
-
-
-def __collapse_buckets_by_batch_id(buckets: Dict) -> Dict:
-    # interleave buckets while trying to maximise shared grad accum chunks
-    batch_ids = [k[0] for k in buckets.keys()]
-    items_by_batch_id = {}
-    for batch_id in batch_ids:
-        items_by_batch_id[batch_id] = __unchunk([b for bucket_key,b in buckets.items() if bucket_key[0] == batch_id])
-    return items_by_batch_id
-
-def __flatten_buckets_preserving_named_batch_adjacency(items_by_batch_id: Dict[str, List[ImageTrainItem]],
-                                                       batch_size: int,
-                                                       grad_accum: int) -> List[ImageTrainItem]:
-    # ensure we don't mix and match aspect ratios by treating each chunk of batch_size images as a single unit to pass to first_fit_decreasing
-    filler_items = __chunk(items_by_batch_id.get(DEFAULT_BATCH_ID, []), batch_size)
-    custom_batched_items = [__chunk(v, batch_size) for k, v in items_by_batch_id.items() if k != DEFAULT_BATCH_ID]
-    neighbourly_chunked_items = first_fit_decreasing(custom_batched_items,
-                                                     batch_size=grad_accum,
-                                                     filler_items=filler_items)
-
-    items: List[ImageTrainItem] = __unchunk(neighbourly_chunked_items)
-    return items
-
 class DataLoaderMultiAspect():
     """
     Data loader for multi-aspect-ratio training and bucketing
@@ -144,8 +110,9 @@ class DataLoaderMultiAspect():
 
         for image_caption_pair in picked_images:
             image_caption_pair.runt_size = 0
-            batch_id = image_caption_pair.batch_id
-            bucket_key = (batch_id, image_caption_pair.target_wh[0], image_caption_pair.target_wh[1])
+            bucket_key = (image_caption_pair.batch_id,
+                          image_caption_pair.target_wh[0],
+                          image_caption_pair.target_wh[1])
             if bucket_key not in buckets:
                 buckets[bucket_key] = []
             buckets[bucket_key].append(image_caption_pair)
@@ -167,14 +134,14 @@ class DataLoaderMultiAspect():
 
         # handle batch_id
         # unlabelled data (no batch_id) is in batches labelled DEFAULT_BATCH_ID.
-        items_by_batch_id = __collapse_buckets_by_batch_id(buckets)
-        items = __flatten_buckets_preserving_named_batch_adjacency(items_by_batch_id,
+        items_by_batch_id = collapse_buckets_by_batch_id(buckets)
+        items = flatten_buckets_preserving_named_batch_adjacency(items_by_batch_id,
                                                                    batch_size=batch_size,
                                                                    grad_accum=grad_accum)
 
         # chunk by effective batch size
         effective_batch_size = batch_size * grad_accum
-        chunks = __chunk(items, effective_batch_size)
+        chunks = chunk(items, effective_batch_size)
         # shuffle, but preserve the last chunk as last if it is incomplete
         last_chunk = None
         if len(chunks[-1]) < effective_batch_size:
@@ -183,7 +150,7 @@ class DataLoaderMultiAspect():
         if last_chunk is not None:
             chunks.append(last_chunk)
         # un-chunk
-        items = __unchunk(chunks)
+        items = unchunk(chunks)
 
         return items
 
@@ -232,3 +199,31 @@ class DataLoaderMultiAspect():
             self.rating_overall_sum += item.caption.rating()
             self.ratings_summed.append(self.rating_overall_sum)
 
+
+def chunk(l: List, chunk_size) -> List:
+    num_chunks = int(math.ceil(float(len(l)) / chunk_size))
+    return [l[i * chunk_size:(i + 1) * chunk_size] for i in range(num_chunks)]
+
+def unchunk(chunked_list: List):
+    return [i for c in chunked_list for i in c]
+
+def collapse_buckets_by_batch_id(buckets: Dict) -> Dict:
+    # interleave buckets while trying to maximise shared grad accum chunks
+    batch_ids = [k[0] for k in buckets.keys()]
+    items_by_batch_id = {}
+    for batch_id in batch_ids:
+        items_by_batch_id[batch_id] = unchunk([b for bucket_key,b in buckets.items() if bucket_key[0] == batch_id])
+    return items_by_batch_id
+
+def flatten_buckets_preserving_named_batch_adjacency(items_by_batch_id: Dict[str, List[ImageTrainItem]],
+                                                       batch_size: int,
+                                                       grad_accum: int) -> List[ImageTrainItem]:
+    # ensure we don't mix and match aspect ratios by treating each chunk of batch_size images as a single unit to pass to first_fit_decreasing
+    filler_items = chunk(items_by_batch_id.get(DEFAULT_BATCH_ID, []), batch_size)
+    custom_batched_items = [chunk(v, batch_size) for k, v in items_by_batch_id.items() if k != DEFAULT_BATCH_ID]
+    neighbourly_chunked_items = first_fit_decreasing(custom_batched_items,
+                                                     batch_size=grad_accum,
+                                                     filler_items=filler_items)
+
+    items: List[ImageTrainItem] = unchunk(neighbourly_chunked_items)
+    return items