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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 set_permissions(filename, uid=None, gid=None, mode=0775):
 """ Set pemissions for given `filename`. Args: filename (str):
 name of the file/directory uid (int, default proftpd):
 user ID - if not set, user ID of `proftpd` is used gid (int):
 group ID, if not set, it is not changed mode (int, default 0775):
 unix access mode """

    if uid is None:
        uid = get_ftp_uid()

    if gid is None:
        gid = -1

    os.chown(filename, uid, gid)
    os.chmod(filename, mode)