Make textbooks in the course definition be stored as data, rather than objects,…

Make textbooks in the course definition be stored as data, rather than objects, and turn them into objects during module instatiation

common/lib/xmodule/xmodule/course_module.py

@@ -22,9 +22,6 @@ class CourseDescriptor(SequenceDescriptor):
             self.book_url = book_url
             self.table_of_contents = self._get_toc_from_s3()
 
-        @classmethod
-        def from_xml_object(cls, xml_object):
-            return cls(xml_object.get('title'), xml_object.get('book_url'))
 
         @property
         def table_of_contents(self):
@@ -57,10 +54,18 @@ class CourseDescriptor(SequenceDescriptor):
 
             return table_of_contents
 
-
     def __init__(self, system, definition=None, **kwargs):
         super(CourseDescriptor, self).__init__(system, definition, **kwargs)
-        self.textbooks = self.definition['data']['textbooks']
+
+        self.textbooks = []
+        for title, book_url in self.definition['data']['textbooks']:
+            try:
+                self.textbooks.append(self.Textbook(title, book_url))
+            except:
+                # If we can't get to S3 (e.g. on a train with no internet), don't break
+                # the rest of the courseware.
+                log.exception("Couldn't load textbook ({0}, {1})".format(title, book_url))
+                continue
 
         self.wiki_slug = self.definition['data']['wiki_slug'] or self.location.course
 
@@ -82,7 +87,6 @@ class CourseDescriptor(SequenceDescriptor):
         #   disable the syllabus content for courses that do not provide a syllabus
         self.syllabus_present = self.system.resources_fs.exists(path('syllabus'))
 
-
     def set_grading_policy(self, policy_str):
         """Parse the policy specified in policy_str, and save it"""
         try:
@@ -94,19 +98,11 @@ class CourseDescriptor(SequenceDescriptor):
             # the error log.
             self._grading_policy = {}
 
-
     @classmethod
     def definition_from_xml(cls, xml_object, system):
         textbooks = []
         for textbook in xml_object.findall("textbook"):
-            try:
-                txt = cls.Textbook.from_xml_object(textbook)
-            except:
-                # If we can't get to S3 (e.g. on a train with no internet), don't break
-                # the rest of the courseware.
-                log.exception("Couldn't load textbook")
-                continue
-            textbooks.append(txt)
+            textbooks = (textbook.get('title'), textbook.get('book_url'))
             xml_object.remove(textbook)
 
         #Load the wiki tag if it exists
@@ -116,7 +112,7 @@ class CourseDescriptor(SequenceDescriptor):
             wiki_slug = wiki_tag.attrib.get("slug", default=None)
             xml_object.remove(wiki_tag)
 
-        definition =  super(CourseDescriptor, cls).definition_from_xml(xml_object, system)
+        definition = super(CourseDescriptor, cls).definition_from_xml(xml_object, system)
 
         definition.setdefault('data', {})['textbooks'] = textbooks
         definition['data']['wiki_slug'] = wiki_slug