Move common code for extractors based in MTV services to a new base class

Removes the duplication of the thumbnail extraction code (only MTVIE needs to override it)

youtube_dl/extractor/southparkstudios.py

@@ -1,15 +1,14 @@
 import re
 
-from .mtv import MTVIE, _media_xml_tag
+from .mtv import MTVServicesInfoExtractor
 
 
-class SouthParkStudiosIE(MTVIE):
+class SouthParkStudiosIE(MTVServicesInfoExtractor):
     IE_NAME = u'southparkstudios.com'
     _VALID_URL = r'(https?://)?(www\.)?(?P<url>southparkstudios\.com/(clips|full-episodes)/(?P<id>.+?)(\?|#|$))'
 
     _FEED_URL = 'http://www.southparkstudios.com/feeds/video-player/mrss'
 
-    # Overwrite MTVIE properties we don't want
     _TESTS = [{
         u'url': u'http://www.southparkstudios.com/clips/104437/bat-daded#tab=featured',
         u'file': u'a7bff6c2-ed00-11e0-aca6-0026b9414f30.mp4',
@@ -19,14 +18,6 @@ class SouthParkStudiosIE(MTVIE):
         },
     }]
 
-    def _get_thumbnail_url(self, uri, itemdoc):
-        search_path = '%s/%s' % (_media_xml_tag('group'), _media_xml_tag('thumbnail'))
-        thumb_node = itemdoc.find(search_path)
-        if thumb_node is None:
-            return None
-        else:
-            return thumb_node.attrib['url']
-
     def _real_extract(self, url):
         mobj = re.match(self._VALID_URL, url)
         url = u'http://www.' + mobj.group(u'url')