Submit checkpoint handler

handler.py

class CheckpointMeHandler(BaseHandler):
    @user_required
    @as_json
    def post(self):
        import json
        from application.models import File, ExerciseCheckpointUser, ExerciseItemUser, \
            ExerciseUser, CourseUser, ExerciseProject, ExerciseItem, Exercise, Course
        from api.restful import current_user
        from google.appengine.ext import ndb
        body_data = json.loads(self.request.body)
        _checkpoint_id = body_data.get("checkpoint_id", None)
        if _checkpoint_id:
            _status = body_data.get("status", None)
            _file = body_data.get("file", None)
            if _status == "passed":
                _current_user = current_user()
                _checkpoint = ndb.Key(urlsafe=_checkpoint_id).get()
                _exercise_checkpoint_user = ExerciseCheckpointUser.get_by_user_and_checkpoint(_current_user
                                                                                              , _checkpoint.key)
                if not _exercise_checkpoint_user:
                    _exercise_checkpoint_user = ExerciseCheckpointUser()
                    _exercise_checkpoint_user.user = _current_user
                    _exercise_checkpoint_user.checkpoint = _checkpoint.key
                if _file:
                    _file = File(content=_file, filename='script')
                    _file.put()
                    _exercise_checkpoint_user.files.append(_file.key)
                _exercise_checkpoint_user.put()
                _project = ExerciseProject.get_by_checkpoint(_checkpoint.key)
                _item = ExerciseItem.get_by_project(_project.key)
                _exercise = Exercise.get_by_exercise_item(_item.key)
                _course = Course.get_by_exercise(_exercise.key)
                _item_user = ExerciseItemUser.get_by_user_and_exercise_item(_current_user, _item.key)
                if not _item_user:
                    _item_user = ExerciseItemUser()
                    _item_user.user = _current_user
                    _item_user.exercise_item = _item.key
                #TODO: Check passed project
                _item_user.current_checkpoint = _checkpoint.key
                if _checkpoint.key not in _item_user.passed_checkpoint:
                    _item_user.passed_checkpoint.append(_checkpoint.key)
                _item_user.put()
                _exercise_user = ExerciseUser.get_by_user_and_exercise(_current_user,_exercise.key)
                if not _exercise_user:
                    _exercise_user = ExerciseUser()
                    _exercise_user.user = _current_user
                    _exercise_user.exercise = _exercise.key
                #TODO: Check passed item
                _exercise_user.current_item = _item.key
                _exercise_user.put()
                _course_user = CourseUser.get_by_user_and_course(_current_user, _course.key)
                if not _course_user:
                    _course_user = CourseUser()
                    _course_user.user = _current_user
                    _course_user.course = _course.key
                _course_user.current_exercise = _exercise.key
                #TODO: Check passed exercise
                _course_user.put()
        return {}