def METHOD_NAME(lfn, redirector="global"):
    """
    Converts a logical file name *lfn* to a physical file name *pfn* using a *redirector*. Valid
    values for *redirector* are defined by :py:attr:`Site.redirectors`.
    """
    if redirector not in Site.redirectors:
        raise ValueError("unknown redirector: {}".format(redirector))
    return "root://{}/{}".format(Site.redirectors[redirector], lfn)