Python script to convert a Linux octal permission number to a text string

perm_to_text.py

def perm_to_text(perm):
    perms = {
        "0": "---",
        "1": "--x",
        "2": "-w-",
        "3": "-wx",
        "4": "r--",
        "5": "r-x",
        "6": "rw-",
        "7": "rwx"
        }
    if len(perm) == 4:
        first = perm[0]
        perm = perm[1:]
    else:
        first = ""

    try:
        outperms = ""
        for p in perm:
            outperms += perms[p]
    except KeyError as e:
        outperms = perm

    if first != "":
        if first == '0':
            pass
        elif first == '1':
            pass
        elif first == '2':
            if outperms[5] == 'x':
                outperms = outperms[:5]+'s'+outperms[6:]
            else:
                outperms = outperms[:5]+'S'+outperms[6:]
        elif first == '4':
            if outperms[2] == 'x':
                outperms = outperms[:2]+'s'+outperms[3:]
            else:
                outperms = outperms[:2]+'S'+outperms[3:]
        else:
            outperms = perm

    return "-"+outperms

import stat
stat.filemode(0o107664) # '-rwSrwSr-T'