Add custom LTI exception.

common/lib/xmodule/xmodule/exceptions.py

@@ -31,3 +31,11 @@ class SerializationError(Exception):
     def __init__(self, location, msg):
         super(SerializationError, self).__init__(msg)
         self.location = location
+
+
+class LTIError(Exception):
+    """
+    An error occured when parsing LTI paramaters from
+    course settings or LTI unit
+    """
+    pass

common/lib/xmodule/xmodule/lti_module.py

@@ -14,6 +14,7 @@ import urllib
 
 from xmodule.editing_module import MetadataOnlyEditingDescriptor
 from xmodule.x_module import XModule
+from xmodule.exceptions import LTIError
 from xmodule.course_module import CourseDescriptor
 from pkg_resources import resource_string
 from xblock.core import String, Scope, List