exception handling with different error codes

Question

I'd like to know how to handle different exceptions that have the same "type". I'm trying to use some code to make a directory:

os.mkdir(target_dir_name)

And I know this can fail for a variety of reasons, for example if the directory already exists:

OSError: [Errno 17] File exists:

or if there's no permissions to create a new dir:

OSError: [Errno 13] Permission denied:

I'd like to tailor my error messages to the specific failure cause, so I came up with the following code:

try:
  os.mkdir(target_dir_name)
except OSError as e:
  if e.errno == 17:
    print "Warning: Directory %s already exists, executing a rebuild" % (target_dir_name)
  elif e.errno == 13:
    sys.exit("Error: Directory "+target_dir_name+" cannot be created incorrect permissions")

but I'd like to do something a little less hardcoded. Is there a Pythonic way I could update my sub-failure checks?

In Python 3.3, there errors got split into distinct types: docs.python.org/3/whatsnew/… — user395760
– user395760, Commented Jul 10, 2013 at 18:10
I haven't found an elegant solution yet since a lot of those exception and error types are so specific with their attributes. So generally in this case I usually do what stackoverflow.com/a/16268642/158111 suggests - wrap specific error handling into a function and avoid repetitive hardcoding. — woozyking
– woozyking, Commented Jul 10, 2013 at 18:12
@delnan - Thanks for the input. This will be a distributed script when I'm done with it and I'm trying not to tie myself down to one version of Python if I can help it. I can't guarantee what everyone will be running, but I figured 2.7.3 would be pretty safe (as that comes standard on the latest stable Ubuntu release) — Mike
– Mike, Commented Jul 10, 2013 at 18:12
2.7.3 is almost as version-locked as you can get. The 2.7 line is the final version of Python 2. Python 2.7.4 and 2.7.5 are bugfix releases, and Python 3 breaks backwards compatibility. — user2357112
– user2357112, Commented Jul 10, 2013 at 18:30

Mike · Accepted Answer · 2013-07-10 19:43:21Z

1

The only information I've found... which I guess is my best answer:

With the errno module I can at least rewrite my current code as:

import errno
#...
except OSError as e:
  if e.errno == errno.EEXIST:
    print "Warning: Directory %s already exists, e..."
  elif e.errno == errno.EACCESS:
    sys.exit("Error: Directory "+target_dir_name+"..."

If I upgrade to python 3.2 there is the much nicer:

except FileExistsError:
  print ("Warning: Directory %s already exists, e...")
except PermissionError:
  sys.exit("Error: Directory "+target_dir_name+"...")

Seems I could do something fancy with using sys.version_info.major and minor to make sure it's at least 3.2 as well.

Hopefully something better will come up...

edited Jul 10, 2013 at 19:43

answered Jul 10, 2013 at 19:37

Mike

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