import: support extraction of bzip2 and gzip tarballs

[cota]

Use case

I'm trying to use beets to import albums from a set of bzip2/gzip tarballs, i.e. .tar.bz2 and .tar.gz files. Would be nice if we could just import them instead of having to extract them first.

Solution

I see that the tarfile module can process tar archives with gzip or bzip2 compression, so hopefully this is not too hard to do. Unfortunately I don't know Python so I cannot provide a patch.

Alternatives

As a workaround I am extracting the tarballs first. Not the end of the world but it would be nice to be able to just point beets to the files, just like we do with rar and zip files.

Thanks for maintaining this great piece of software!

[jackwilsdon]

Have you tried importing a .tar.bz2 or .tar.gz? It looks like we should already support it from the source:

beets/beets/importer.py

Lines 1037 to 1038 in 19ab28e

	from tarfile import is_tarfile, TarFile
	cls._handlers.append((is_tarfile, TarFile))

[cota]

Note that TarFile only works for uncompressed tar archives. Quoting from /usr/lib/python3.8/tarfile.py:

    def __init__(self, name=None, mode="r", fileobj=None, format=None,
            tarinfo=None, dereference=None, ignore_zeros=None, encoding=None,
            errors="surrogateescape", pax_headers=None, debug=None,
            errorlevel=None, copybufsize=None):
        """Open an (uncompressed) tar archive `name'. `mode' is either 'r' to
           read from an existing archive, 'a' to append data to an existing
           file or 'w' to create a new file overwriting an existing one. `mode'
           defaults to 'r'.
[...]

The method that we want is TarFile.open, not the constructor:

   def open(cls, name=None, mode="r", fileobj=None, bufsize=RECORDSIZE, **kwargs):
        """Open a tar archive for reading, writing or appending. Return
           an appropriate TarFile class.

           mode:
           'r' or 'r:*' open for reading with transparent compression
[...]

I'll send a patch. Please double check the tests, this is the first time I write anything in Python and I've given up trying to get the necessary packages :(