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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 walk_revctrl(dirname='', ff=''):
 """Return files found by the file-finder 'ff'. """

    file_finder = None
    items = []

    if not ff:
        distutils.log.error('No file-finder passed to walk_revctrl')
        sys.exit(1)

    for ep in pkg_resources.iter_entry_points('setuptools.file_finders'):
        if ff == ep.name:
            distutils.log.info('using %s file-finder', ep.name)
            file_finder = ep.load()
            finder_items = []
            with pythonpath_off():
                for item in file_finder(dirname):
                    if not basename(item).startswith(('.svn', '.hg', '.git')):
                        finder_items.append(item)
            distutils.log.info('%d files found', len(finder_items))
            items.extend(finder_items)

    if file_finder is None:
        distutils.log.error('Failed to load %s file-finder; setuptools-%s extension missing?',
            ff, 'subversion' if ff == 'svn' else ff)
        sys.exit(1)

    # Returning a non-empty list prevents egg_info from reading the
    # existing SOURCES.txt
    return items or ['']