'Return a BlockRecordList from previously serialized json.'

@classmethod
def from_json(cls, blockrecord_json):

    data = json.loads(blockrecord_json)
    course_key = CourseKey.from_string(data['course_key'])
    block_dicts = data['blocks']
    record_generator = (BlockRecord(locator=UsageKey.from_string(block['locator']).replace(course_key=course_key), weight=block['weight'], raw_possible=block['raw_possible'], graded=block['graded']) for block in block_dicts)
    return cls(record_generator, course_key, version=data['version'])
