'Sets the object\'s course_keys attribute from the `courses` parameter.
If that parameter isn\'t furnished, loads all course_keys from the
modulestore.
Filters out course_keys in the `skip` parameter, if provided.
Args:
courses: A list of string serializations of course keys.
For example, ["course-v1:org+course+run"].
skip: Also a list of string serializations of course keys.'

@classmethod
def create(cls, courses=None, skip=None):

    if courses:
        course_keys = [CourseKey.from_string(course.strip()) for course in courses]
    else:
        course_keys = [course.id for course in modulestore().get_course_summaries()]
    if (skip is not None):
        skip_keys = [CourseKey.from_string(course.strip()) for course in skip]
        course_keys = [course_key for course_key in course_keys if (course_key not in skip_keys)]
    return cls(course_keys)
