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The tar format allows to have memeber files whose path has a leading "./":
$ echo > foo
$ tar cf bar.tar ./foo
$ tar tf bar.tar 
./foo
However the tarfile module doesn't allow this:
>>> from StringIO import StringIO
>>> from tarfile import TarInfo, TarFile
>>> info = TarInfo("./foo")
>>> fd = open("bar.tar", "w")
>>> tar = TarFile.open(fileobj=fd, mode="w")
>>> tar.addfile(info, "")
>>> tar.close()
then:
$ tar tf bar.tar 
foo
So in practice the tarfile module forces the removal of leading "./"'s.
In particular this is a problem when creating .deb files (dpkg) programmatically as these contains tar files with members with a leading "./".

Please note that even if unpacking such a tar might be semantically equivalent to a version which strips out the "./" prefix, it should be possible to create a tar with valid path names such as these.
In the case of debs, for instance, the files inside the tarball may contain expected path names, which means that some (badly done, perhaps) tools could *expect* the file to be exactly that which is created by the standard tools (e.g. "./debian/control"), and break down once it's not found.
With this in mind, it would indeed be nice to be able to use paths prefixed with "./" in Python's tarfile.

This is a duplicate of issue6054 which has been fixed in Python 2.7 (r74571).
(Hi, Gustavo!)

Thanks for the prompt reply! Cool to know this is already fixed.

Indeed, nice use of the time machine! :-)
Thanks Lars!