code: def filter_extant_exports(client, bucket, prefix, days, start, end=None):
      
      end = end or datetime.now()
      # days = [start + timedelta(i) for i in range((end-start).days)]
      try:
          tag_set = client.get_object_tagging(Bucket=bucket, Key=prefix).get('TagSet', [])
      except ClientError as e:
          if e.response['Error']['Code'] != 'NoSuchKey':
              raise
          tag_set = []
      tags = {t['Key']: t['Value'] for t in tag_set}
  
      if 'LastExport' not in tags:
          return sorted(days)
      last_export = parse(tags['LastExport'])
      if last_export.tzinfo is None:
          last_export = last_export.replace(tzinfo=tzutc())
      return [d for d in sorted(days) if d > last_export]
docs: Filter days where the bucket already has extant export keys.