[youtube] Fix extraction.

[youtube-dl] / youtube_dl / extractor / frontendmasters.py

diff --git a/youtube_dl/extractor/frontendmasters.py b/youtube_dl/extractor/frontendmasters.py
index 770db46d0d63a0bdebea2d362850155b55044d93..f1db33fb161f13d2b2fe6e09d327c04247444945 100644 (file)
--- a/youtube_dl/extractor/frontendmasters.py
+++ b/youtube_dl/extractor/frontendmasters.py
@@ -11,6 +11,7 @@ from ..compat import (
 from ..utils import (
     ExtractorError,
     parse_duration,
+    url_or_none,
     urlencode_postdata,
 )
 
@@ -80,7 +81,7 @@ class FrontendMastersPageBaseIE(FrontendMastersBaseIE):
         chapters = []
         lesson_elements = course.get('lessonElements')
         if isinstance(lesson_elements, list):
-            chapters = [e for e in lesson_elements if isinstance(e, compat_str)]
+            chapters = [url_or_none(e) for e in lesson_elements if url_or_none(e)]
         return chapters
 
     @staticmethod
@@ -93,8 +94,8 @@ class FrontendMastersPageBaseIE(FrontendMastersBaseIE):
         chapter_number = None
         index = lesson.get('index')
         element_index = lesson.get('elementIndex')
-        if (isinstance(index, int) and isinstance(element_index, int) and
-                index < element_index):
+        if (isinstance(index, int) and isinstance(element_index, int)
+                and index < element_index):
             chapter_number = element_index - index
         chapter = (chapters[chapter_number - 1]
                    if chapter_number - 1 < len(chapters) else None)