os.lstat : proper way to do this

[m1k3b0]

I'm converting from Perl to Python, so I'm learning the basics -
please be gentle!

In Perl, I can lstat($file) whether $file exists or not:
lstat($file);
unless (-e _) {
print STDERR "$file: No such file or directory\n";
}
unless (-l _) {
print STDERR "$file: Not a symbolic link\n";
}

The lstat() returns normally whether the file exists or not, and I
check for existence with the "-e" conditional. Then I go on and check
other modes.

In Python,if I os.lstat(file) and file doesn't exist, I get an error
from within the module:
OSError: [Errno 2] No such file or directory: '/etc/xxx'

I can check first with os.path.exists(file), but then I'm doing two
stat() type calls which is inefficient (especially when we're talking
thousands of files).

I want to be able to do something like this:
mode = os.lstat(file)[ST_MODE]
if not mode:
print >> sys.stderr, file, ": No such file or directory"
if not S_ISLNK(mode):
print >> sys.stderr, file, ": Not a symbolic link"

Of course, this isn't valid. How can I do this efficiently without
getting "no such file" error?

Thanks!
mikebo

 

[MRAB]

I'm converting from Perl to Python, so I'm learning the basics -
please be gentle!

In Perl, I can lstat($file) whether $file exists or not:
lstat($file);
unless (-e _) {
print STDERR "$file: No such file or directory\n";
}
unless (-l _) {
print STDERR "$file: Not a symbolic link\n";
}

The lstat() returns normally whether the file exists or not, and I
check for existence with the "-e" conditional. Then I go on and check
other modes.

In Python,if I os.lstat(file) and file doesn't exist, I get an error
from within the module:
OSError: [Errno 2] No such file or directory: '/etc/xxx'

I can check first with os.path.exists(file), but then I'm doing two
stat() type calls which is inefficient (especially when we're talking
thousands of files).

I want to be able to do something like this:
mode = os.lstat(file)[ST_MODE]
if not mode:
print >> sys.stderr, file, ": No such file or directory"
if not S_ISLNK(mode):
print >> sys.stderr, file, ": Not a symbolic link"

Of course, this isn't valid. How can I do this efficiently without
getting "no such file" error?

Just catch the exception:

try:
mode = os.lstat(file).st_mode # An alternative way.
# If we get here then the file does exist.
if not S_ISLNK(mode):
print >> sys.stderr, file, ": Not a symbolic link"
except OSError, e:
if e.errno == 2:
# File doesn't exist.
print >> sys.stderr, file, ": No such file or directory"
else:
# Failed for some other reason.


BTW, "file" happens to be the name of one of the build-ins, so try to
use something else, eg. "file_path".