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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 has_been_completed_by(poll, user):
 """ This will return a boolean indicating if the passed user has already voted in the given poll. Usage:: """

    user_votes = TopicPollVote.objects.filter(
        poll_option__poll=poll)
    if user.is_anonymous:
        forum_key = get_anonymous_user_forum_key(user)
        user_votes = user_votes.filter(anonymous_key=forum_key) if forum_key \
            else user_votes.none()
    else:
        user_votes = user_votes.filter(voter=user)
    return user_votes.exists()