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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 import_ownertrust(cls, trustdb=None):
 """Import ownertrust from a trustdb file. :param str trustdb: The path to the trustdb.gpg file. If not given, defaults to :file:`trustdb.gpg` in the current GnuPG homedir. """

    if trustdb is None:
        trustdb = os.path.join(cls.homedir, 'trustdb.gpg')

    import_proc = cls._open_subprocess(['--import-ownertrust'])

    try:
        tdb = open(trustdb, 'rb')
    except (OSError, IOError):
        log.error("trustdb file %s does not exist!" % trustdb)

    _util._threaded_copy_data(tdb, import_proc.stdin)
    import_proc.wait()