ImageFields now include PIL error messages if invalid error (#353)

docs/changelog.rst

@@ -5,6 +5,7 @@ Changelog
 
 Changes in 0.8.2
 ================
+- ImageFields now include PIL error messages if invalid error (#353)
 - Fixed hashing of EmbeddedDocuments (#348)
 - Added lock when calling doc.Delete() for when signals have no sender (#350)
 - Reload forces read preference to be PRIMARY (#355)

mongoengine/fields.py

@@ -1259,8 +1259,8 @@ class ImageGridFsProxy(GridFSProxy):
         try:
             img = Image.open(file_obj)
             img_format = img.format
-        except:
+        except Exception, e:
-            raise ValidationError('Invalid image')
+            raise ValidationError('Invalid image: %s' % e)
 
         if (field.size and (img.size[0] > field.size['width'] or
                             img.size[1] > field.size['height'])):

tests/fields/file_tests.py

@@ -269,6 +269,17 @@ class FileTest(unittest.TestCase):
 
         TestImage.drop_collection()
 
+        with tempfile.TemporaryFile() as f:
+            f.write(b("Hello World!"))
+            f.flush()
+
+            t = TestImage()
+            try:
+                t.image.put(f)
+                self.fail("Should have raised an invalidation error")
+            except ValidationError, e:
+                self.assertEquals("%s" % e, "Invalid image: cannot identify image file")
+
         t = TestImage()
         t.image.put(open(TEST_IMAGE_PATH, 'rb'))
         t.save()