human
Solve the following python programming problem given the following code:
@gen.engine
def ProcessFiles(logs_store, merged_store, logs_paths, filenames, dry_run, callback):
assistant
#Here is the Python program you requested.

    """Process each file contained in \filenames\. Returns a list of successfully processed file names.
    """
    processed_files = []
    day_instance_logs = {}
    s3_base = logs_paths.MergedDirectory()
    @gen.engine
    def _AddEntry(instance, entry, callback):
        'Given    a    single    log    entry,    validate    it,    find    (or    create)    the    corresponding    LocalLogMerge    and    add    it.'
        if (not entry):
            callback()
            return
        parsed = logs_util.ParseLogLine(entry)
        if (not parsed):
            callback()
            return
        (day, _, _, _) = parsed
        day_log = None
        if ((instance, day) not in day_instance_logs):
            day_instance_logs[(instance, day)] = log_merger.LocalLogMerge(merged_store, [day, instance], s3_base)
            day_log = day_instance_logs[(instance, day)]
            (yield gen.Task(day_log.FetchExistingFromS3))
        day_log = day_instance_logs[(instance, day)]
        day_log.Append(entry)
        callback()
    @gen.engine
    def _ProcessOneFile(instance, contents, callback):
        'Iterate    over    a    raw    log    file.    Any    line    that    does    not    start    with    a    date    in    the    form    YYYY-MM-DD    is    considered\n                part    of    a    multi-line    entry.\n                TODO(marc):    this    will    break    horribly    if    we    ever    have    multiple    processes/threads    logging    to    the    same    file.\n                '
        buf = cStringIO.StringIO(contents)
        buf.seek(0)
        entry = ''
        while True:
            line = buf.readline()
            if (not line):
                (yield gen.Task(_AddEntry, instance, entry))
                break
            if (line.startswith(('    ', ' DCTB ')) or (logs_util.ParseLogLine(line) is None)):
                entry += ('    ' + line.strip())
            else:
                (yield gen.Task(_AddEntry, instance, entry))
                entry = line.strip()
        buf.close()
        callback()
    for filename in filenames:
        instance =...