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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 submission_stream(reddit_session, subreddit, limit=None, verbosity=1):
 """Indefinitely yield new submissions from the provided subreddit. Submissions are yielded from oldest to newest. :param reddit_session: The reddit_session to make requests from. In all the examples this is assigned to the variable ``r``. :param subreddit: Either a subreddit object, or the name of a subreddit. Use `all` to get the submissions stream for all submissions made to reddit. :param limit: The maximum number of submissions to fetch in a single iteration. When None, fetch all available submissions (reddit limits this to 1000 (or multiple of 1000 for multi-subreddits). If this number is too small, submissions may be missed. Since there isn't a limit to the number of submissions that can be retrieved from r/all, the limit will be set to 1000 when limit is None. :param verbosity: A number that controls the amount of output produced to stderr. <= 0: no output; >= 1: output the total number of submissions processed and provide the short-term number of submissions processed per second; >= 2: output when additional delays are added in order to avoid subsequent unexpected http errors. >= 3: output debugging information regarding the submission stream. (Default: 1) """

    if six.text_type(subreddit).lower() == "all":
        if limit is None:
            limit = 1000
    if not hasattr(subreddit, 'reddit_session'):
        subreddit = reddit_session.get_subreddit(subreddit)
    return _stream_generator(subreddit.get_new, limit, verbosity)