Added tuple option for durations

PIL/GifImagePlugin.py

@@ -361,7 +361,7 @@ def _save(im, fp, filename, save_all=False):
             for im_frame in ImageSequence.Iterator(imSequence):
                 encoderinfo = im.encoderinfo.copy()
                 im_frame = _convert_mode(im_frame)
-                if isinstance(duration, list):
+                if isinstance(duration, (list, tuple)):
                     encoderinfo["duration"] = duration[frame_count]
                 frame_count += 1
 

Tests/test_file_gif.py

@@ -290,6 +290,8 @@ class TestFileGif(PillowTestCase):
             Image.new('L', (100, 100), '#111'),
             Image.new('L', (100, 100), '#222'),
         ]
+
+        #duration as list
         im_list[0].save(
             out,
             save_all=True,
@@ -305,6 +307,24 @@ class TestFileGif(PillowTestCase):
             except EOFError:
                 pass
 
+        # duration as tuple
+        im_list[0].save(
+            out,
+            save_all=True,
+            append_images=im_list[1:],
+            duration=tuple(duration_list)
+        )
+        reread = Image.open(out)
+
+        for duration in duration_list:
+            self.assertEqual(reread.info['duration'], duration)
+            try:
+                reread.seek(reread.tell() + 1)
+            except EOFError:
+                pass
+
+
+
     def test_number_of_loops(self):
         number_of_loops = 2