[Tutor] making a function work with os.path.walk()

[Christopher Spears]

I wrote a function called get_size(n,dir,files).  This
is the code:

import os

def get_size(n,dir,files):
    files_of_size = {}; sizes = [];
    biggest_files = []; files_sizes = [];
    files = map(os.path.join,[dir] * len(files),files)
    files = filter(lambda x: not os.path.isdir(x)
                   and not os.path.islink(x),
os.listdir(dir))

    for f in files:
       
files_of_size.setdefault(os.path.getsize(f),[]).append(f)

    sizes = files_of_size.keys()
    sizes.sort(); sizes.reverse();
    for s in sizes:
        biggest_files.append([files_of_size[s],s])

    while n > 0:
        print biggest_files[n-1]
        n = n - 1

The function takes a number n and a directory name and
prints out the n largest files.  However when I try to
use it with os.path.walk() I get the following result.

>>> os.path.walk('.',get_size,3)
[['Unit5.doc'], 22016L]
[['Unit8.doc'], 22528L]
[['Unit6.doc'], 23552L]

Traceback (most recent call last):
  File "<pyshell#4>", line 1, in -toplevel-
    os.path.walk('.',get_size,3)
  File "C:\Python23\lib\ntpath.py", line 333, in walk
    walk(name, func, arg)
  File "C:\Python23\lib\ntpath.py", line 327, in walk
    func(arg, top, names)
  File "C:\Documents and Settings\Christstopher
Spears\My Documents\python\unit9.question1c.py", line
11, in get_size
   
files_of_size.setdefault(os.path.getsize(f),[]).append(f)
  File "C:\Python23\lib\ntpath.py", line 228, in
getsize
    return os.stat(filename).st_size
OSError: [Errno 2] No such file or directory:
'DSCN4432.JPG'

I cannot decipher the error message.  From what I can
gather, the function works fine in its current
directory, but seems to be having problems with the
other directory in the current directory.  What I find
odd is that it claims that the .JPG doesn't exist, but
it is in the other directory.  Suggestions, hints,
etc?

-Chris