python: file system abstracted as dictionary

file_system.py

import glob
import os

class Directory:
    def __init__(self, path = '/'):
        self.path = path

    def __getitem__(self, key):
        fn = os.path.join(self.path, key)
        if os.path.exists(fn):
            return File(fn)
        else:
            raise IndexError

    def __str__(self):
        return 'Directory for %s' % self.path

    def __iter__(self):
        def child(fn):
            path = os.path.join(self.path, fn)
            return File(path)
        return (child(fn) for fn in os.listdir(self.path))

class UnreadableFile:
    def __init__(self, fn):
        self.fn = fn

    def __str__(self):
        return 'unreadable file %s' % self.fn

def File(fn):
    if os.path.isdir(fn):
        return Directory(fn)
    else:
        try:
            return open(fn)
        except:
            return UnreadableFile(fn)

root_dir = Directory('/')
for fn in root_dir:
    print fn

log  = root_dir['var']['log']['system.log']
print next(log).strip()
print next(log).strip()
print next(log).strip()
print next(log).strip()