[Tutor] Cannot fix OSError

[Nick Lunt]

Hi Folks,

this is my first posting to the list, although I have been snooping for
a couple of weeks ;)

I've recently started to learn Python and so far I'm having great fun.

Anyway, here's my problem, first off here's the program:

# code
import tarfile, sys, os

if len(sys.argv) <= 2:
        print 'Error:', sys.argv[0], ' <tarfile.tar> <list of files>
        sys.exit(1)

tfile = sys.argv[1]

totar = []
for f in sys.argv[2:]:
        if os.access(f, os.R_OK): # NOTE1
                totar.append(f)
        else:
                print 'Could not access', f, 'to tar'


tf = tarfile.TarFile(tfile, 'w')
for f in totar:
        tf.add(f)

tf.close

# end code

This works fine until it encounters a file that I am not allowed to access, in which case it gives me this error:

# error
Traceback (most recent call last):
  File "./tar.py", line 31, in ?
    tf.add(f)
  File "/usr/lib/python2.3/tarfile.py", line 1220, in add
    self.add(os.path.join(name, f), os.path.join(arcname, f))
  File "/usr/lib/python2.3/tarfile.py", line 1220, in add
    self.add(os.path.join(name, f), os.path.join(arcname, f))
  File "/usr/lib/python2.3/tarfile.py", line 1219, in add
    for f in os.listdir(name):
OSError: [Errno 13] Permission denied: '/etc/skel/tmp'

# end error

I could trap it in a try/except OSError block, but I'd like to know why the line NOTE1 does not simply cause the program to skip the unreadable file and continue ?

>From the python interpreter 'os.access('/file/i/cant/read', os.R_OK)' returns False so I expected my 'if' on line NOTE1 to sort that out.

If someone could just explain to me where I'm going wrong I'd be extremely greatful.

Many thanks
Nick.