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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 atlasdb_sync_zonefiles( db, start_block, zonefile_dir, atlas_state, validate=True, end_block=None, path=None, con=None ):
 """ Synchronize atlas DB with name db NOT THREAD SAFE """

    ret = None
    with AtlasDBOpen(con=con, path=path) as dbcon:
        ret = atlasdb_queue_zonefiles( dbcon, db, start_block, zonefile_dir, validate=validate, end_block=end_block )
        atlasdb_cache_zonefile_info( con=dbcon )

    if atlas_state:
        # it could have been the case that a zone file we already have was re-announced.
        # if so, then inform any storage listeners in the crawler thread that this has happened
        # (such as the subdomain system).
        crawler_thread = atlas_state['zonefile_crawler']
        for zfinfo in filter(lambda zfi: zfi['present'], ret):
            log.debug('Store re-discovered zonefile {} at {}'.format(zfinfo['zonefile_hash'], zfinfo['block_height']))
            crawler_thread.store_zonefile_cb(zfinfo['zonefile_hash'], zfinfo['block_height'])

    return ret