Fix broken progress bar (#524)

- Fix broken update calculation
- Make progress bar use the neat `unit_scale` feature
  of tqdm

Author: kohr-h

torchvision/datasets/utils.py

@@ -5,10 +5,12 @@
 from tqdm import tqdm
 
 
-def gen_bar_updator(pbar):
+def gen_bar_updater(pbar):
     def bar_update(count, block_size, total_size):
-        pbar.total = total_size / block_size
-        pbar.update(count)
+        if pbar.total is None and total_size:
+            pbar.total = total_size
+        progress_bytes = count * block_size
+        pbar.update(progress_bytes - pbar.n)
 
     return bar_update
 
@@ -47,13 +49,19 @@ def download_url(url, root, filename, md5):
     else:
         try:
             print('Downloading ' + url + ' to ' + fpath)
-            urllib.request.urlretrieve(url, fpath, reporthook=gen_bar_updator(tqdm()))
+            urllib.request.urlretrieve(
+                url, fpath,
+                reporthook=gen_bar_updater(tqdm(unit='B', unit_scale=True))
+            )
         except:
             if url[:5] == 'https':
                 url = url.replace('https:', 'http:')
                 print('Failed download. Trying https -> http instead.'
                       ' Downloading ' + url + ' to ' + fpath)
-                urllib.request.urlretrieve(url, fpath)
+                urllib.request.urlretrieve(
+                    url, fpath,
+                    reporthook=gen_bar_updater(tqdm(unit='B', unit_scale=True))
+                )
 
 
 def list_dir(root, prefix=False):