You can use TarFile.getnames() like this:
#!/usr/bin/env python3
import tarfile
tarf = tarfile.open('foo.tar.gz', 'r:gz')
print(tarf.getnames())
http://docs.python.org/3.3/library/tarfile.html#tarfile.TarFile.getnames
And if you want mtime values you can use getmembers().
print([(member.name, member.mtime) for member in tarf.getmembers()])