Fine-grained OSError subclasses or cross-platform errnos?

[John J. Lee]

Today, I wanted to do something like this:

def nr_files(dirNam e)
try:
return len(os.listdir( dirName))
except OSError, e:
if e.errno == errno.ENOENT:
return 0
else:
raise

In other words, I wanted to trap only the case of missing directory
(and not, for example, insufficient permissions), and I wanted to do
it in the EAFP style.

The problem is that errno is not cross-platform. Neither is there any
subclass of OSError that I can conveniently catch to figure out what
went wrong.

Is there any better way of doing this?

If not, why not?
John