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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_submission(self, submissionid, user_check=True):
 """ Get a submission from the database """

        sub = self._database.submissions.find_one({'_id': ObjectId(submissionid)})
        if user_check and not self.user_is_submission_owner(sub):
            return None
        return sub