[utils] Fix intlist_to_bytes in Python 2 (#4181)

test/test_utils.py

@@ -46,6 +46,7 @@ from youtube_dl.utils import (
     escape_url,
     js_to_json,
     get_filesystem_encoding,
+    intlist_to_bytes,
 )
 
 
@@ -350,5 +351,10 @@ class TestUtil(unittest.TestCase):
         self.assertEqual(clean_html('a:\nb'), 'a: b')
         self.assertEqual(clean_html('a:\n   "b"'), 'a:    "b"')
 
+    def test_intlist_to_bytes(self):
+        self.assertEqual(
+            intlist_to_bytes([0, 1, 127, 128, 255]),
+            b'\x00\x01\x7f\x80\xff')
+
 if __name__ == '__main__':
     unittest.main()

youtube_dl/utils.py

@@ -843,10 +843,7 @@ def bytes_to_intlist(bs):
 def intlist_to_bytes(xs):
     if not xs:
         return b''
-    if isinstance(chr(0), bytes):  # Python 2
-        return ''.join([chr(x) for x in xs])
-    else:
-        return bytes(xs)
+    return struct.pack('%dB' % len(xs), *xs)
 
 
 # Cross-platform file locking