def runAsEffectiveUser(euid, egid, function, *args, **kwargs):
    """
    Run the given function wrapped with seteuid/setegid calls.

    This will try to minimize the number of seteuid/setegid calls, comparing
    current and wanted permissions

    @param euid: effective UID used to call the function.
    @type euid: C{int}

    @type egid: effective GID used to call the function.
    @param egid: C{int}

    @param function: the function run with the specific permission.
    @type function: any callable

    @param *args: arguments passed to C{function}
    @param **kwargs: keyword arguments passed to C{function}
    """
    uid, gid = os.geteuid(), os.getegid()
    if uid == euid and gid == egid:
        return function(*args, **kwargs)
    else:
        if uid != 0 and (uid != euid or gid != egid):
            os.seteuid(0)
        if gid != egid:
            os.setegid(egid)
        if euid != 0 and (euid != uid or gid != egid):
            os.seteuid(euid)
        try:
            return function(*args, **kwargs)
        finally:
            if euid != 0 and (uid != euid or gid != egid):
                os.seteuid(0)
            if gid != egid:
                os.setegid(gid)
            if uid != 0 and (uid != euid or gid != egid):
                os.seteuid(uid)

    Run the given function wrapped with seteuid/setegid calls.

    This will try to minimize the number of seteuid/setegid calls, comparing
    current and wanted permissions

    @param euid: effective UID used to call the function.
    @type euid: C{int}

    @type egid: effective GID used to call the function.
    @param egid: C{int}

    @param function: the function run with the specific permission.
    @type function: any callable

    @param *args: arguments passed to C{function}
    @param **kwargs: keyword arguments passed to C{function}
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/util.py