instagram: handle user-provided alt text

fixes #159

https://instagram-press.com/blog/2018/11/28/creating-a-more-accessible-instagram/

granary/instagram.py

@@ -66,6 +66,11 @@
 _last_rate_limited = None      # datetime
 _last_rate_limited_exc = None  # requests.HTTPError
 
+AUTO_ALT_TEXT_PREFIXES = (
+  'No photo description available.',
+  'Image may contain: ',
+)
+
 
 class Instagram(source.Source):
   """Instagram source class. See file docstring and Source class for details."""
@@ -609,6 +614,14 @@ def media_to_object(self, media):
       self._mention_tags_from_content(content)
     }
 
+    # alt text
+    # https://instagram-press.com/blog/2018/11/28/creating-a-more-accessible-instagram/
+    alt = media.get('accessibility_caption')
+    if alt and not any(alt.startswith(prefix) for prefix in AUTO_ALT_TEXT_PREFIXES):
+      for att in object['attachments']:
+        for img in att.get('image', []):
+          img['displayName'] = alt
+
     for version in ('standard_resolution', 'low_resolution', 'thumbnail'):
       image = media.get('images', {}).get(version)
       if image:

granary/tests/test_instagram.py

@@ -620,6 +620,7 @@ def tag_uri(name):
         'id': '1455954810972087680',
         'dimensions': {'height': 1080, 'width': 1080},
         'display_url': 'https://instagram.fsnc1-2.fna.fbcdn.net/t51.2885-15/s1080x1080/e35/16906679_776417269184045_871950675452362752_n.jpg',
+        'accessibility_caption': 'this is my alt text',
         'is_video': False,
         'edge_media_to_tagged_user': {'edges': []},
       },
@@ -953,6 +954,7 @@ def tag_uri(name):
   'url': 'https://www.instagram.com/p/ABC123/',
   'image': [{
     'url': 'https://instagram.fsnc1-2.fna.fbcdn.net/t51.2885-15/s1080x1080/e35/16906679_776417269184045_871950675452362752_n.jpg',
+    'displayName': 'this is my alt text',
     'width': 1080,
     'height': 1080,
   }],
@@ -1623,6 +1625,19 @@ def test_html_to_activities_multi_photo(self):
     self.assert_equals([HTML_MULTI_PHOTO_ACTIVITY], activities)
     self.assertIsNone(viewer)
 
+  def test_html_to_activities_multi_photo_omit_auto_alt_text(self):
+    multi = copy.deepcopy(HTML_MULTI_PHOTO_PAGE)
+    multi['entry_data']['PostPage'][0]['graphql']['shortcode_media']\
+        ['edge_sidecar_to_children']['edges'][1]['node']['accessibility_caption'] = \
+        instagram.AUTO_ALT_TEXT_PREFIXES[1] + 'foo bar'
+    html = HTML_HEADER + json.dumps(multi) + HTML_FOOTER
+
+    expected = copy.deepcopy(HTML_MULTI_PHOTO_ACTIVITY)
+    del expected['object']['attachments'][1]['image'][0]['displayName']
+
+    activities, _ = self.instagram.html_to_activities(html)
+    self.assert_equals([expected], activities)
+
   def test_html_to_activities_missing_profile_picture_external_url(self):
     data = copy.deepcopy(HTML_FEED)
     data['config']['viewer']['profile_pic_url'] = None