Question

I’m attempting to use Python’s tarfile module to extract a tar.gz archive.

I’d like the extraction to overwrite any target files it they already exist – this is tarfile’s normal behaviour.

However, I’m hitting a snitch in that some of the files have write-protection on (e.g. chmod 550).

The tarfile.extractall() operation actually fails:

IOError: [Errno 13] Permission denied '/foo/bar/file'

If I try to delete the files from the normal command-line, I can do it, I just need to answer a prompt:

$ rm <filename>
rm: <filename>: override protection 550 (yes/no)? yes

The normal GNU tar utility also handles these files effortlessly – it just overwrites them when you extract.

My user is the owner of the files, so it wouldn’t be hard to recursively chmod the target files before running tarfile.extractall. Or I can use shutil.rmtree to blow away the target beforehand, which is the workaround I’m using now.. However, that feels a little hackish.

Is there a more Pythonic way of handle overwriting read-only files within tarfile, using exceptions, or something similar?

Answer 1

You could loop over the members of the tarball and extract / handle errors on each file:

In a modern version of Python I’d use the with statement:

import os, tarfile

with tarfile.TarFile('myfile.tar', 'r', errorlevel=1) as tar:
    for file_ in tar:
        try:
            tar.extract(file_)
        except IOError as e:
            os.remove(file_.name)
            tar.extract(file_)
        finally:
            os.chmod(file_.name, file_.mode)

If you can’t use with just replace the with statement block with:

tarball = tarfile.open('myfile.tar', 'r', errorlevel=1)
for file_ in tar:

If your tar ball is gzipped there’s a quick shortcut to handle that with just:

tarfile.open('myfile.tar.gz', 'r:gz')

It would be nicer if tarfile.extractall had an overwrite option.