Added support for generators when using append_images for WEBP

PIL/WebPImagePlugin.py

@@ -167,7 +167,7 @@ class WebPImageFile(ImageFile.ImageFile):
 
 def _save_all(im, fp, filename):
     encoderinfo = im.encoderinfo.copy()
-    append_images = encoderinfo.get("append_images", [])
+    append_images = list(encoderinfo.get("append_images", []))
 
     # If total frame count is 1, then save using the legacy API, which
     # will preserve non-alpha modes

Tests/test_file_webp_animated.py

@@ -65,12 +65,7 @@ class TestFileWebpAnimation(PillowTestCase):
         are visually similar to the originals.
         """
 
-        temp_file = self.tempfile("temp.webp")
-        frame1 = Image.open('Tests/images/anim_frame1.webp')
-        frame2 = Image.open('Tests/images/anim_frame2.webp')
-        frame1.save(temp_file,
-            save_all=True, append_images=[frame2], lossless=True)
-
+        def check(temp_file):
             im = Image.open(temp_file)
             self.assertEqual(im.n_frames, 2)
 
@@ -83,6 +78,23 @@ class TestFileWebpAnimation(PillowTestCase):
             im.load()
             self.assert_image_equal(im, frame2.convert("RGBA"))
 
+        frame1 = Image.open('Tests/images/anim_frame1.webp')
+        frame2 = Image.open('Tests/images/anim_frame2.webp')
+
+        temp_file1 = self.tempfile("temp.webp")
+        frame1.copy().save(temp_file1,
+            save_all=True, append_images=[frame2], lossless=True)
+        check(temp_file1)
+
+        # Tests appending using a generator
+        def imGenerator(ims):
+            for im in ims:
+                yield im
+        temp_file2 = self.tempfile("temp_generator.webp")
+        frame1.copy().save(temp_file2,
+            save_all=True, append_images=imGenerator([frame2]), lossless=True)
+        check(temp_file2)
+
     def test_timestamp_and_duration(self):
         """
         Try passing a list of durations, and make sure the encoded