Use TarFS to read and write .tar files.
Here's how you could create a tar file:
>>> from fs import open_fs
>>> with open_fs('tar://test.tar.gz', create=True) as tarfs:
... tarfs.settext('foo', 'bar')
And here is how you would read it back.
>>> from fs import open_fs
>>> with open_fs('tar://test.tar.gz') as tarfs:
... print(tarfs.gettext('foo'))
'bar'
See TarFS docs for more information.