def tweets_to_file(tweets, tweetfile, append=False, pure_json=False, pretty
    =False):
    """
    Exports a collection (iterable) of tweets to given file. Exports tweets in mongoDB
    extended special bson format. 
    To append to given tweetfile, pass append=True
    For pure json (not bson object rep), pass pure_json=True. 
    To pretty-print json (value-per-line and spacing), pass pretty=True
    """
    raise DeprecationWarning(
        "'tweets_to_file' is deprecated. Use 'tweets_to_bson' or 'tweets_to_json' instead."
        )
    return
