[udemy] Detect non free courses (Closes #8138)

youtube_dl/extractor/udemy.py

@@ -11,6 +11,7 @@ from ..utils import (
     float_or_none,
     int_or_none,
     sanitized_Request,
+    unescapeHTML,
 )
 
 
@@ -19,8 +20,6 @@ class UdemyIE(InfoExtractor):
     _VALID_URL = r'https?://www\.udemy\.com/(?:[^#]+#/lecture/|lecture/view/?\?lectureId=)(?P<id>\d+)'
     _LOGIN_URL = 'https://www.udemy.com/join/login-popup/?displayType=ajax&showSkipButton=1'
     _ORIGIN_URL = 'https://www.udemy.com'
-    _SUCCESSFULLY_ENROLLED = '>You have enrolled in this course!<'
-    _ALREADY_ENROLLED = '>You are already taking this course.<'
     _NETRC_MACHINE = 'udemy'
 
     _TESTS = [{
@@ -37,15 +36,21 @@ class UdemyIE(InfoExtractor):
     }]
 
     def _enroll_course(self, webpage, course_id):
-        enroll_url = self._search_regex(
+        checkout_url = unescapeHTML(self._search_regex(
+            r'href=(["\'])(?P<url>https?://(?:www\.)?udemy\.com/payment/checkout/.+?)\1',
+            webpage, 'checkout url', group='url', default=None))
+        if checkout_url:
+            raise ExtractorError(
+                'Course %s is not free. You have to pay for it before you can download.'
+                'Use this URL to confirm purchase: %s' % (course_id, checkout_url), expected=True)
+
+        enroll_url = unescapeHTML(self._search_regex(
             r'href=(["\'])(?P<url>https?://(?:www\.)?udemy\.com/course/subscribe/.+?)\1',
-            webpage, 'enroll url', group='url',
-            default='https://www.udemy.com/course/subscribe/?courseId=%s' % course_id)
-        webpage = self._download_webpage(enroll_url, course_id, 'Enrolling in the course')
-        if self._SUCCESSFULLY_ENROLLED in webpage:
-            self.to_screen('%s: Successfully enrolled in' % course_id)
-        elif self._ALREADY_ENROLLED in webpage:
-            self.to_screen('%s: Already enrolled in' % course_id)
+            webpage, 'enroll url', group='url', default=None))
+        if enroll_url:
+            webpage = self._download_webpage(enroll_url, course_id, 'Enrolling in the course')
+            if '>You have enrolled in' in webpage:
+                self.to_screen('%s: Successfully enrolled in the course' % course_id)
 
     def _download_lecture(self, course_id, lecture_id):
         return self._download_json(